Previously, the server would attempt taking port/socket in worker
process, and if it was taken, fail, which made the master process
create a new worker. This led to really high CPU usage if the
streaming API was started when the port or socket were not
available.

Now, before clustering (forking) into worker processes, a test
server is created and then removed to check if it can be done.

* Add check for missing tag param in streaming API

Fixes error:

```
TypeError: Cannot read property 'toLowerCase' of undefined
at app.get (.../streaming/index.js:493:50)
```

* Fix code style issues

* Add conversations API

* Add web UI for conversations

* Add test for conversations API

* Add tests for ConversationAccount

* Improve web UI

* Rename ConversationAccount to AccountConversation

* Remove conversations on block and mute

* Change last_status_id to be a denormalization of status_ids

* Add optimistic locking

GET /api/v1/streaming/health

Answers with OK. Fix #8337

* Support UNIX domain socket for streaming service without using PORT

The use of UNIX domain socket for streaming service was not officially supported,
but it was made unofficial to use by setting a path to PORT.
From now on, SOCKET will be used just like setting for puma.

* Hundle relative path

* Added a timeline for Direct statuses
* Lists all Direct statuses you've sent and received
* Displayed in Getting Started
* Streaming server support for direct TL

* Changes to match other timelines in 2.0

On an unhandled worker exception, we should log the exception
and exit with nonzero status, instead of letting workers
silently fail and restarting them in an endless loop.

Note: we previously tried to handle the `'error'` signal.
That's not a signal Node fires; my patch traps `'uncaughtException'`,
which is what the code was _trying_ to do.

* make it possible to stream public timelines without authorization

* Fix

* Make eslint allow `value == null`

* Remove redundant line

* Improve style and revert .eslintrc.yml

* Fix streamWsEnd

* Show IP address instead of (anonymous user)

* Add missing semicolon

* 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

* Restore streaming API output format

Regression from #4090

* Remove whitespace

* more free pgconfig for streaming by .env

* fix wrong default values

* database.yml read ENV as same as streaming server

* Fix errorMiddleware

* Add "eslint-disable-line no-unused-vars"

by using Array.prototype.indexOf instead

* Add redis key "subscribed:timeline:#{account.id}" to indicate active streaming API listeners exists.

* Add endpoint for notification only stream.

* Run PushUpdateWorker only for users uses Streaming API now.

* Move close hander streamTo(Http/Ws) -> stream(Http/Ws)End (Deal with #3370)

* Add stream type for stream start log message.

* Return 401 for an authentication error on WebSocket

* Use upgradeReq instead of a custom object

* Don't stream toots from users who have blocked the recipient user

This filter was already applied on the `/api/v1/timelines/public` API, but
not yet for the Streaming API.

* Boosted status' account_id doesn't need for filtering in streaming/index.js

This filtering is only for public/hashtag timelines, but boosts already filtered on FanOutOnWriteService because those timelines don't show boosts.

* Improve streaming API cluster logging

* Less verbose error middleware logging (stack trace useless there)

* Fix error logging

* Prevent potential issue

* Add missing "done()" in catch of Promise.all, websocket heartbeat re-implemented like in example

* I actually forgot a done(), the absolute madman

This location varies across postgres installations, and it seems like the pg
package knows how to guess correctly on each system.

Resolves #2780

* Add semi to ESLint rules

* Add padded-blocks to ESLint rules

* Add comma-dangle to ESLint rules

* add config/webpack and storyboard

* add streaming/

* yarn test:lint -- --fix