Issue #216064 by Xano, idflood, drifter, Artusamak, ygerasimov, sun, ParisLiakos, Cottser, TravisCarden, marcingy, floretan, catch, tedbow: Entity form "Delete" button triggers server-side + HTML5 form validation; change "Delete" button to a link.

Issue #2028035 by vladan.me, ceng, Berdir, David Hernández, larowlan: Expand CustomBlockInterface with methods.

Issue #2074037 by Wim Leers, effulgentsia: Add drupalPostUrl() — drupalPost()/drupalPostAjax() are for forms only, D8 JS performs non-form HTTP requests.

Issue #1983682 by tim.plunkett, h3rj4n, larowlan: Convert applicable custom_block_menu() entries to use _entity_form() in routing.yml.

Issue #1620010 by dawehner, ParisLiakos, plach, jibran: Move LANGUAGE constants to the Language class.