Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

Issue #2005716 by tim.plunkett, msonnabaum, dawehner, alexpott, effulgentsia: Promote EntityType to a domain object.

Issue #1653026 by damiankloip, alexpott, sun, tim.plunkett, dawehner, mtift: Fixed All configuration values are stored as strings.

Issue #1855402 by andypost, fubhy, tim.plunkett, dawehner, sun: Add generic weighting (tabledrag) support for config entities (ConfigEntityListController).

Issue #2064557 by tim.plunkett: Improve strange coupling in EntityListControllers by improving buildRow() and buildHeader().

Issue #2005778 by webflo, naxoc, penyaskito, andypost, vijaycs85, plopesc, maggo: Convert language_admin_overview_form() to a Controller.