* Add structure for lists

* Add list timeline streaming API

* Add list APIs, bind list-account relation to follow relation

* Add API for adding/removing accounts from lists

* Add pagination to lists API

* Add pagination to list accounts API

* Adjust scopes for new APIs

- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope

* Add test for wrong user context on list timeline

* Clean up tests

Thread resolving is one of the few tasks that isn't retried on failure.
One common cause for failure of this task is a well-connected user replying to
a toot from a little-connected user on a small instance: the small instance
will get many requests at once, and will often fail to answer requests within
the 10 seconds timeout used by Mastodon.

This changes makes the ThreadResolveWorker retry a few times, with a
rapidly-increasing time before retries and large random contribution in order
to spread the load over time.

Fix #5597

* Clean up reblog-tracking sets from FeedManager

Builds on #5419, with a few minor optimizations and cleanup of sets
after they are no longer needed.

* Update tests, fix multiply-reblogged case

Previously, we would have lost the fact that a given status was
reblogged if the displayed reblog of it was removed, now we don't.

Also added tests to make sure FeedManager#trim cleans up our reblog
tracking keys, fixed up FeedCleanupScheduler to use the right loop,
and fixed the test for it.

* Keep references to all reblogs of a status on home feed

When inserting reblog: Add to set of reblogs of this status on
the feed, if original status was present in the feed, add it to
that set as well.

When removing a reblog: Remove it from that set. Take random
remaining item from the set. If one exists, re-insert it into feed,
otherwise do not re-insert anything.

Fix #4210

* When original is removed, toss out reblog references

* Close connection when succeeded posting

* Update webmock

- Rename Mastodon::TimestampIds into Mastodon::Snowflake for clarity
- Skip for statuses coming from inbox, aka delivered in real-time
- Skip for statuses that claim to be from the future

* Improve error handling on LinkCrawlWorker

* Ignore TimeoutError and InvalidURIError too
* Record errors to debug log
* Enable dead job queue on LinkCrawlWorker

Since most of acceptable errors were already ignored, only our side issue should go to dead job queue.

* Ignore all http gem errors

- A successful delivery cancels it out
- An incoming delivery from account of the inbox cancels it out

Reply distribution is proceed by Sidekiq, so replied status may be deleted before this.

* Add scheduled worker to purge old user IPs

* Use ruby 1.9 hash syntax

* Revert "Enable UniqueRetryJobMiddleware even when called from sidekiq worker (#4836)"

This reverts commit 6859d4c0.

* Revert "Do not execute the job with the same arguments as the retry job (#4814)"

This reverts commit be7ffa2d.

* Make RefollowWorker ActivityPub-only to avoid potential identifier mismatches

* Don't call RefollowWorker on new accounts

* Whenever a remote keypair changes, unfollow them and re-subscribe to them

In Mastodon (it could be different for other OStatus or AP-enabled software),
a keypair change is indicative of whole user (or instance) data loss. In this
situation, the “new” user might be different, and almost certainly has an empty
followers list. In this case, Mastodon instances will disagree on follower
lists, leading to unreliable delivery and “shadow followers”, that is users
believed by a remote instance to be followers, without the affected user
knowing.

Drawbacks of this change are:
1. If an user legitimately changes public key for some reason without losing
   data (not possible in Mastodon at the moment), they will have their remote
   followers unsubscribed/re-subscribed needlessly.
2. Depending of the number of remote followers, this may generate quite some
   traffic.
3. If the user change is an attempt at usurpation, the remote followers will
   unknowingly follow the usurper. Note that this is *not* a change of
   behavior, Mastodon already behaves like that, although delivery might be
   unreliable, and the usurper would not have known the former user's
   followers.

* Rename ResubscribeWorker to RefollowWorker

* Process followers in batches

When a new user confirms their e-mail, bootstrap their home timeline
by automatically following a set of accounts. By default, all local
admin accounts (that are unlocked). Can be customized by new admin
setting (comma-separated usernames, local and unlocked only)

* Decouple Status#local? from uri being nil

* Replace on-the-fly URI generation with stored URIs

- Generate URI in after_save hook for local statuses
- Use static value in TagManager when available, fallback to tag format
- Make TagManager use ActivityPub::TagManager to understand new format
- Adjust tests

* Use other heuristic for locality of old statuses, do not perform long query

* Exclude tombstone stream entries from Atom feed

* Prevent nil statuses from landing in Pubsubhubbub::DistributionWorker

* Fix URI not being saved (#4818)

* Add more specs for Status

* Save generated uri immediately

and also fix method order to minimize diff.

* Fix alternate HTML URL in Atom

* Fix tests

* Remove not-null constraint from statuses migration to speed it up

* Forward ActivityPub creates that reply to local statuses

* Fix test

* Fix wrong signers

Requires moving Atom rendering from DistributionWorker (where
`stream_entry.status` is already nil) to inline (where
`stream_entry.status.destroyed?` is true) and distributing that.

Unfortunately, such XML renderings can no longer be easily chained
together into one payload of n items.

* Add handling of Linked Data Signatures in payloads

* Add a way to sign JSON, fix canonicalization of signature options

* Fix signatureValue encoding, send out signed JSON when distributing

* Add missing security context

* ActivityPub migration procedure

Once one account is detected as going from OStatus to ActivityPub,
invalidate WebFinger cache for other accounts from the same domain

* Unsubscribe from PuSH updates once we receive an ActivityPub payload

* Re-subscribe to PuSH unless already unsubscribed, regardless of protocol

*Note: OStatus URIs are invalid for ActivityPub. But we have them for
as long as we want to keep old OStatus-sourced content and as long as
we remain OStatus-compatible.*

- In Announce handling, if object URI is not a URL, fallback to object URL
- Do not use specialized ThreadResolveWorker, rely on generalized handling
- When serializing notes, if parent's URI is not a URL, use parent's URL

* Deliver ActivityPub Like

* Deliver ActivityPub Undo-Like

* Deliver ActivityPub Create/Announce activities

* Deliver ActivityPub creates from mentions

* Deliver ActivityPub Block/Undo-Block

* Deliver ActivityPub Accept/Reject-Follow

* Deliver ActivityPub Undo-Follow

* Deliver ActivityPub Follow

* Deliver ActivityPub Delete activities

Incidentally fix #889

* Adjust BatchedRemoveStatusService for ActivityPub

* Add tests for ActivityPub workers

* Add tests for FollowService

* Add tests for FavouriteService, UnfollowService and PostStatusService

* Add tests for ReblogService, BlockService, UnblockService, ProcessMentionsService

* Add tests for AuthorizeFollowService, RejectFollowService, RemoveStatusService

* Add tests for BatchedRemoveStatusService

* Deliver updates to a local account to ActivityPub followers

* Minor adjustments

* Add ActivityPub inbox

* Handle ActivityPub deletes

* Handle ActivityPub creates

* Handle ActivityPub announces

* Stubs for handling all activities that need to be handled

* Add ActivityPub actor resolving

* Handle conversation URI passing in ActivityPub

* Handle content language in ActivityPub

* Send accept header when fetching actor, handle JSON parse errors

* Test for ActivityPub::FetchRemoteAccountService

* Handle public key and icon/image when embedded/as array/as resolvable URI

* Implement ActivityPub::FetchRemoteStatusService

* Add stubs for more interactions

* Undo activities implemented

* Handle out of order activities

* Hook up ActivityPub to ResolveRemoteAccountService, handle
Update Account activities

* Add fragment IDs to all transient activity serializers

* Add tests and fixes

* Add stubs for missing tests

* Add more tests

* Add more tests

* Add destination informations to exception on SubscribeWorker and DeliveryWorker.

* Simplify delivery error message.

* Prevent changing Exception type...

* fix typo.