* Raise an error for remote url in StatusFinder

Previous implementation had allowed remote url with status id which also exists on local.

Then that bug leads /api/web/embed to return wrong embed url.

* Fix oembed_controller_spec

* Make PreviewCard records reuseable between statuses

**Warning!** Migration truncates preview_cards tablec

* Allow a wider thumbnail for link preview, display it in horizontal layout (#4648)

* Delete preview cards files before truncating

* Rename old table instead of truncating it

* Add mastodon:maintenance:remove_deprecated_preview_cards

* Ignore deprecated_preview_cards in schema definition

* Fix null behaviour

* Don't process ActivityPub payload if signature is invalid

* Fix style issue

* Forward ActivityPub creates that reply to local statuses

* Fix test

* Fix wrong signers

- Use statuses controller for embeds instead of stream entries controller
- Prefer /@:username/:id/embed URL for embeds
- Use /@:username as author_url in OEmbed
- Add follow link to embeds which opens web intent in new window
- Use redis cache in development
- Cache entire embed

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

* Allow multiple pinned statuses to be shown and make them be ordered by pinned date

* Set timestamps NOT NULL

* Make single-line pinned_statuses

* Spec for pinned_statuses

* Remove redundant empty line

* Pinned statuses

* yarn manage:translations

* Process Create / Announce activity in FetchRemoteStatusService

* Use activity URL in ActivityPub for reblogs

* Redirect to the original status on StatusesController#show

- Section it into "Development" area
- Improve UI of application form, index, and details

* Add Mastodon::Source.url

* Update spec

* Refactor

Move things frmo Mastodon::Source to Mastodon::Version

* Add code for creating/managing apps to settings section

* Add specs for app changes

* Fix controller spec

* Fix view file I pasted over by mistake

* Add locale strings. Add 'my apps' to nav

* Add Client ID/Secret to App page. Add some visual separation

* Fix rubocop warnings

* Fix embarrassing typo

I lost an `end` statement while fixing a merge conflict.

* Add code for creating/managing apps to settings section

- Add specs for app changes
- Add locale strings. Add 'my apps' to nav
- Add Client ID/Secret to App page. Add some visual separation
- Fix some bugs/warnings

* Update to match code standards

* Trigger notification

* Add warning about not sharing API secrets

* Tweak spec a bit

* Cleanup fixture creation by using let!

* Remove unused key

* Add foreign key for application<->user

* Fallback to OStatus in FetchAtomService

* Skip activity+json link if that activity is Person without inbox
* If unsupported activity was detected and all other URLs failed, retry with ActivityPub-less Accept header

* Allow mention to OStatus account in ActivityPub

* Don't update profile with inbox-less Person object

*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

* use existing inflections instead of custom helper

* use ActiveSupport versions

* Show what protocol used for in admin/accounts#index

* Add frozen_string_literal

* Add support for searching AP users

* use JsonLdHelper

* 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

* feat: Cache status height to avoid expensive renders

* feat: Escape content and emojify in reducers

* fix(css): Remove backface-visibility: hidden from .scrollable

* fix(statuses): Avoid creating DOMParses inside a loop

* Refactored Avatar and AvatarOverlay (DRY) to have 'account' as prop.
Also removed animate attribute from compose navigation bar, which should
have never been there. Added test for avatar overlay.

* fix broken tests

* god dammit another bug in tests! travis please let this pass

* formatting in avatar overlay