Issue #2498691 by cilefen, mesch, deepakaryan1988, RavindraSingh, honzakuchar, darol100, kattekrab, Cottser, David_Rothstein: "Install and set as default" link on the Appearance page doesn't work

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2389455 by hussainweb, AjitS, Mile23, subhojit777, tibbsa, Ayesh: Clean-up system module test members - ensure property definition and use of camelCase naming convention

Issue #2142653 by corbacho, sqndr, LewisNyman, floretan, BarisW, G-raph, JamesLefrère, lokapujya, LoMo, Outi: Change default logo filetype to .svg and add an SVG version of Druplicon

Issue #2395395 by alexpott, effulgentsia, Gábor Hojtsy: TestBase lacks a config method to be used consistently in tests

Issue #2183983 by Gábor Hojtsy, vijaycs85, Berdir, Wim Leers, webflo, alexpott: Find hidden configuration schema issues

Issue #2350823 by lauriii, jhedstrom, Tim Bozeman, cilefen, davidhernandez, inqui, Cottser, xjm: Use the Classy theme in the Testing profile

Issue #2324055 by dawehner, cilefen, znerol: Split up the module manager into runtime information and extension information

Issue #2329501 by alexpott, mdrummond, davidhernandez | Cottser: Add classy.info.yml to core, set Classy as base theme for Bartik and Seven.

Issue #2329303 by tim.plunkett, dawehner: Fixed Use the right request when determining the theme on a 403 page.

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

Issue #1067408 by alexpott, Jalandhar, jessebeach, Désiré, neetu morwani, dawehner, sun: Themes do not have an installation status.

This reverts commit ae8be3cc.

Issue #1954892 by dawehner, David_Rothstein, tim.plunkett: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Revert "Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system."

This reverts commit fc04601c.

Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Issue #1199946 by alexpott, fubhy, bojanz, steinmb, chx, catch: Fixed Disabled modules are broken beyond repair so the 'disable' functionality needs to be removed.

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

Issue #1856766 by chx, Berdir, heyrocker, kim.pepper: Convert file_public_path() to the new settings system (make it not configurable via UI or YAML).

Issue #2011578 by mortendk, tlattimore, Cottser, soulston: Markup for Stark's page.html.twig + maintenance-page.html.twig.

Issue #1829224 by alexpott, pfrenssen, vijaycs85, lirantal: Convert the 'theme_default()' variable to CMI.

Issue #1496480 by mrf, disasm, kbasarab, pfrenssen, cam8001, typhonius, Letharion, ACF, vijaycs85, heyrocker, Berdir, alexpott: Convert file system settings to the new configuration system.