This commit introduces support for AccountMigration federation message
receive. It covers the cases when the new home pod for a user is remote
respective to the recepient pod of the message. It also allows to initiate
migration locally by a podmin from the rails console. This will give the
pods a possibility to understand the account migration event on the
federation level and thus future version which will implement migration
will be backward compatible with the pods starting from this commit.

Also remove `disconnect_contacts` methods, because contacts are already
removed with aspects memberships in `before_destroy`.

Although this is contrary to rails best-practises, we cannot provide a schema.rb that works for both MySQL and PostgreSQL, so we have no choice. Our migrations are maintained, so it should always be possible to get back to a "clean" database schema anyway.

The hashes don't work properly with rails 5, there are different classes
loaded when called from the rails engine with missing inheritance.

Also the hashes never worked well with spring.

This commit introduces changes to the user data export archive format.
This extends data set which is included in the archive. This data can be
then imported to other pods when this feature is implemented.

Also the commit adds the archive format json schema. ATM it is used in
automatic tests only, but in future it will also be used to validate
incoming archives.

This class is capable of quering a list of people from authors of given posts that are non-contacts of a given
user.

This class implements methods that allow to query relayables (comments, likes, participations,
poll_participations) of other people for posts of the given person.

This class allows to query posts where a person made any activity (submitted comments,
likes, participations or poll participations).

`Rails.application.assets` is only available when `config.assets.compile`
is true (which is false in production). So the old way with a separate
rake task doesn't work in production. But we can get the filename of the
precompiled file from `Rails.application.assets_manifest.assets`.

This improves the main stream when you have less or inactive contacts
and ignored an active person that posts many posts with tags. When the
person is only removed after collecting all post ids, you don't see
posts with tags from other people.

Needed for diaspora/diaspora_federation#64

Related to diaspora/diaspora_federation#27

Related to diaspora/diaspora_federation#32

Related to diaspora/diaspora_federation#30

Related to #36

We don't need to change new to old syntax when we receive a post from a
newer pod, since we can handle the new syntax. This is only needed when
sending it to older pods.

related to #7392

fixes #7317

closes #7322

And update config for new/updated cops.

Fixes #5765, fixes #5815, supersedes #6099.

closes #7350

fixes #7269

* fallback to diaspora ID when person is not found
* fix filter_people when the person is not found
* write some more tests

Because } is not compatible with the regex.