Issue #1925660 by ACF, tim.plunkett, mtift, heddn, Cottser: Convert system's system_config_form() to SystemConfigFormBase.
Issue follow-up #927138 by manarth, handrus, David_Rothstein: Fail image generation with 404 instead of 500, when source file is missing.
Issue #1938430 by shanethehat, steveoliver, Fabianx: Don't add a default theme hook class in template_preprocess().
Issue #1847582 by amateescu: Create a foreign key to the target entity type base type in Entity-reference.
Issue #1975354 by dawehner: Fixed hook_hook_info() might be invoked even the namespace hasn't been registered yet.
Issue #1992834 by alexpott: Fixed Unnecessarily setting up the array of priority formats for content negotiation within a loop.
Issue #1991092 by David_Rothstein: Fixed 'Edit shortcuts' link in the toolbar points to a nonexistent page (as does the 'add shortcuts' link on an empty shortcut set).
Issue #1972260 by ParisLiakos, marcingy: Convert aggregator_admin_refresh_feed() to a new style controller.
Issue #1990732 by joelpittet | andymartha: Fixed template_preprocess_comment() is preparing the parent's author with the wrong comment's uid.
Issue #1978964 by sanchiz: Convert admin/config/user-interface/shortcut/manage/%shortcut_set()/edit to a Controller.
Issue #1974580 by nod_, Wim Leers: Introduce domReady to remove jQuery dependency from drupal.js and clean it up.
Issue #1904932 by dawehner, damiankloip, YesCT: Fixed Cannot remove a handler from the 'rearrange' popup.
Issue #1912606 by jastraat, gollyg, Cottser, joelpittet: Remove theme_views_view_grouping() function.
Issue #1988614 by aroq: Adjust hook_options_list_alter() example in options.api.php to use ->id() instead of ->id.
