Issue #1829170 by LinL, socketwench, vijaycs85, mtift, LittleCoding, andypost, dawehner, ianmthomasuk: Convert the Maintenance Theme variable to settings.

Issue #2038135 by RobLoach, donquixote, Crell, ParisLiakos, catch: Use the Composer autoloader to make everything simpler.

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 #1934716 followup by hackwater: [Followup] Merge system.fast_404 config object into system.performance.

Issue #1971860 by arh1, shanethehat, Fabianx: Document that Twig debug mode can cause automated tests to fail

Issue #1798832 by andreiashu, Berdir, heyrocker, aspilicious, johan.gant, typhonius, ACF: Convert https to .

Issue #1906506 by David_Rothstein,  steveoliver: Fix documentation in default.settings.php for Twig debugging

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

Issue #1855208 by bryanbraun, jessebeach: Added Toolbar tray needs to fix to top of screen on scroll.

Issue #1922814 by Berdir, Damien Tournoud, pwolanin, David_Rothstein, Heine, Bèr Kessels: Fixed Denial-of-service vulnerabiility in Image module.

Issue #1784846 by beltofte, Floydm: Standardize capitalization on actions in operations in shortcut: 'list links', 'edit set', 'delete set', 'edit, 'delete'.

Issue #1906506 by Fabianx, steveoliver, Cottser: Added Twig settings implementation: Show theme hook / template suggestions in HTML comments.

Issue #1833516 by Berdir, chx, catch, webchick: Add $settings for low-level configuration - move things out of .

Issue #1814086 by samhassell, fgm: Convert autoloader_mode in drupal_classloader() to its own global.

Issue #1824778 by vijaycs85, ACF, pcambra, cam8001: Covert css_gzip_compression() and js_gzip_compression() variables to CMI system.

Issue #1828612 by David_Rothstein: Fixed hook_views_query_substitutions() missing from hook_hook_info().

Issue #1828612 by dawehner, damiankloip: Fixed hook_views_query_substitutions() missing from hook_hook_info().

Issue #1539940 by jwilson3, infiniteluke, mrf, ryanissamson: Fix up README files to encourage good placement of themes, modules, and profiles

Issue #1436814 by gary4gar, kid_icarus, webchick, droplet, andypost: Fixed Fast 404 'Not found' pages are missing a doctype.

Issue #1772708 by alexpott, sun, chx, catch, beejeebus: Fixed The configuration directories can not be outside of DRUPAL_ROOT.

Revert "Issue #1772708 by alexpott: Fixed The configuration directories can not be outside of DRUPAL_ROOT."

This reverts commit e003e4c5.

This reverts commit 81666e2b. Sorry, did NOT mean to push that; was testing the CMI UI patch.