* Add followed_by? to account_interactions

* Add RemoveFromFollowersService

* Fix AccountBatch to use RemoveFromFollowersService

* Add remove from followers API

* Fix followers synchronization mechanism not working when URI has empty path

To my knowledge, there is no current implementation on the fediverse
that can use bare domains (e.g., actor is at https://example.org instead of
something like https://example.org/actor) that also plans to support the
followers synchronization mechanism. However, Mastodon's current implementation
would exclude such accounts from followers list.

Also adds tests and rename them to reflect the proper method names.

* Move url prefix regexp to its own constant

* Add support for followers synchronization on the receiving end

Check the `collectionSynchronization` attribute on `Create` and `Announce`
activities and synchronize followers from provided collection if possible.

* Add tests for followers synchronization on the receiving end

* Add support for follower synchronization on the sender's end

* Add tests for the sending end

* Switch from AS attributes to HTTP header

Replace the custom `collectionSynchronization` ActivityStreams attribute by
an HTTP header (`X-AS-Collection-Synchronization`) with the same syntax as
the `Signature` header and the following fields:
- `collectionId` to specify which collection to synchronize
- `digest` for the SHA256 hex-digest of the list of followers known on the
   receiving instance (where “receiving instance” is determined by accounts
   sharing the same host name for their ActivityPub actor `id`)
- `url` of a collection that should be fetched by the instance actor

Internally, move away from the webfinger-based `domain` attribute and use
account `uri` prefix to group accounts.

* Add environment variable to disable followers synchronization

Since the whole mechanism relies on some new preconditions that, in some
extremely rare cases, might not be met, add an environment variable
(DISABLE_FOLLOWERS_SYNCHRONIZATION) to disable the mechanism altogether and
avoid followers being incorrectly removed.

The current conditions are:
1. all managed accounts' actor `id` and inbox URL have the same URI scheme and
   netloc.
2. all accounts whose actor `id` or inbox URL share the same URI scheme and
   netloc as a managed account must be managed by the same Mastodon instance
   as well.

As far as Mastodon is concerned, breaking those preconditions require extensive
configuration changes in the reverse proxy and might also cause other issues.

Therefore, this environment variable provides a way out for people with highly
unusual configurations, and can be safely ignored for the overwhelming majority
of Mastodon administrators.

* Only set follower synchronization header on non-public statuses

This is to avoid unnecessary computations and allow Follow-related
activities to be handled by the usual codepath instead of going through
the synchronization mechanism (otherwise, any Follow/Undo/Accept activity
would trigger the synchronization mechanism even if processing the activity
itself would be enough to re-introduce synchronization)

* Change how ActivityPub::SynchronizeFollowersService handles follow requests

If the remote lists a local follower which we only know has sent a follow
request, consider the follow request as accepted instead of sending an Undo.

* Integrate review feeback

- rename X-AS-Collection-Synchronization to Collection-Synchronization
- various minor refactoring and code style changes

* Only select required fields when computing followers_hash

* Use actor URI rather than webfinger domain in synchronization endpoint

* Change hash computation to be a XOR of individual hashes

Makes it much easier to be memory-efficient, and avoid sorting discrepancy issues.

* Marginally improve followers_hash computation speed

* Further improve hash computation performances by using pluck_each

* Add bell button

Fix #4890

* Remove duplicate type from post-deployment migration

* Fix legacy class type mappings

* Improve query performance with better index

* Fix validation

* Remove redundant index from notifications

* Add option to overwrite imported data

Fix #7465

* Add import for domain blocks

* Keep notification when muting_notifications is true

* Retrun mute object

* Fix test

* Allow hiding of reblogs from followed users

This adds a new entry to the account menu to allow users to hide
future reblogs from a user (and then if they've done that, to show
future reblogs instead).

This does not remove or add historical reblogs from/to the user's
timeline; it only affects new statuses.

The API for this operates by sending a "reblogs" key to the follow
endpoint. If this is sent when starting a new follow, it will be
respected from the beginning of the follow relationship (even if
the follow request must be approved by the followee). If this is
sent when a follow relationship already exists, it will simply
update the existing follow relationship. As with the notification
muting, this will now return an object ({reblogs: [true|false]}) or
false for each follow relationship when requesting relationship
information for an account. This should cause few issues due to an
object being truthy in many languages, but some modifications may
need to be made in pickier languages.

Database changes: adds a show_reblogs column (default true,
non-nullable) to the follows and follow_requests tables. Because
these are non-nullable, we use the existing MigrationHelpers to
perform this change without locking those tables, although the
tables are likely to be small anyway.

Tests included.

See also <https://github.com/glitch-soc/mastodon/pull/212>.

* Rubocop fixes

* Code review changes

* Test fixes

This patchset closes #648 and resolves #3271.

* Rubocop fix

* Revert reblogs defaulting in argument, fix tests

It turns out we needed this for the same reason we needed it in muting:
if nil gets passed in somehow (most usually by an API client not passing
any value), we need to detect and handle it.

We could specify a default in the parameter and then also catch nil, but
there's no great reason to duplicate the default value.

* Add tests for class methods of AccountInteractions

* Add tests for instance methods of AccountInteractions

* Add a hide_notifications column to mutes

* Add muting_notifications? and a notifications argument to mute!

* block notifications in notify_service from hard muted accounts

* Add specs for how mute! interacts with muting_notifications?

* specs testing that hide_notifications in mutes actually hides notifications

* Add support for muting notifications in MuteService

* API support for muting notifications (and specs)

* Less gross passing of notifications flag

* Break out a separate mute modal with a hide-notifications checkbox.

* Convert profile header mute to use mute modal

* Satisfy eslint.

* specs for MuteService notifications params

* add trailing newlines to files for Pork :)

* Put the label for the hide notifications checkbox in a label element.

* Add a /api/v1/mutes/details route that just returns the array of mutes.

* Define a serializer for /api/v1/mutes/details

* Add more specs for the /api/v1/mutes/details endpoint

* Expose whether a mute hides notifications in the api/v1/relationships endpoint

* Show whether muted users' notifications are muted in account lists

* Allow modifying the hide_notifications of a mute with the /api/v1/accounts/:id/mute endpoint

* make the hide/unhide notifications buttons work

* satisfy eslint

* In probably dead code, replace a dispatch of muteAccount that was skipping the modal with launching the mute modal.

* fix a missing import

* add an explanatory comment to AccountInteractions

* Refactor handling of default params for muting to make code cleaner

* minor code style fixes oops

* Fixed a typo that was breaking the account mute API endpoint

* Apply white-space: nowrap to account relationships icons

* Fix code style issues

* Remove superfluous blank line

* Rename /api/v1/mutes/details -> /api/v2/mutes

* Don't serialize "account" in MuteSerializer

Doing so is somewhat unnecessary since it's always the current user's account.

* Fix wrong variable name in api/v2/mutes

* Use Toggle in place of checkbox in the mute modal.

* Make the Toggle in the mute modal look better

* Code style changes in specs and removed an extra space

* Code review suggestions from akihikodaki

Also fixed a syntax error in tests for AccountInteractions.

* Make AddHideNotificationsToMute Concurrent

It's not clear how much this will benefit instances in practice, as the
number of mutes tends to be pretty small, but this should prevent any
blocking migrations nonetheless.

* Fix up migration things

* Remove /api/v2/mutes