Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- README.md
  discarded upstream changes
- app/controllers/api/v1/bookmarks_controller.rb
  finally merged upstream, some code style fixes
  and slightly changed pagination code
- app/controllers/application_controller.rb
  changed upstream to always return HTML error pages
  slight conflict caused by theming code
- app/models/bookmark.rb
  finally merged upstream, no real conflict
- spec/controllers/api/v1/bookmarks_controller_spec.rb
  finally merged upstream, slightly changed pagination code

db/migrate/20180831171112_create_bookmarks.rb

@@ -0,0 +1,17 @@
+class CreateBookmarks < ActiveRecord::Migration[5.1]
+  def change
+    create_table :bookmarks do |t|
+      t.references :account, null: false
+      t.references :status, null: false
+
+      t.timestamps
+    end
+
+    safety_assured do
+      add_foreign_key :bookmarks, :accounts, column: :account_id, on_delete: :cascade
+      add_foreign_key :bookmarks, :statuses, column: :status_id, on_delete: :cascade
+    end
+
+    add_index :bookmarks, [:account_id, :status_id], unique: true
+  end
+end