Add bookmarks (#7107)

* Add backend support for bookmarks

Bookmarks behave like favourites, except they aren't shared with other
users and do not have an associated counter.

* Add spec for bookmark endpoints

* Add front-end support for bookmarks

* Introduce OAuth scopes for bookmarks

* Add bookmarks to archive takeout

* Fix migration

* Coding style fixes

* Fix rebase issue

* Update bookmarked_statuses to latest UI changes

* Update bookmark actions to properly reflect status changes in state

* Add bookmarks item to single-column layout

* Make active bookmarks red

app/models/concerns/account_interactions.rb

@@ -186,6 +186,10 @@ module AccountInteractions
     status.proper.favourites.where(account: self).exists?
   end
 
+  def bookmarked?(status)
+    status.proper.bookmarks.where(account: self).exists?
+  end
+
   def reblogged?(status)
     status.proper.reblogs.where(account: self).exists?
   end