* 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

* Add a StatusFilter class to identify visibility of statuses by accounts

* Extract StatusThreadingConcern from Status

* Clarify purpose of checking for nil account

* Move specs for account finder methods to concern spec

* Move account finder methods to concern

* Improve spec wording

* Use more explicit comparison to ensure correct return value

* Add coverage for .find_local! and .find_remote!

* Add some methods to the finder

* Use arel on matching_username method

* Avoid ternary in matching domain method

* Simplify finder methods

* Use an AccountFinder class to simplify lookup