Issue #2368987 by Wim Leers, Berdir, Schnitzel, epari.siva, bircher, vijaycs85, likin: Move internal page caching to a module to avoid relying on config get on runtime

Issue #2459971 by Gábor Hojtsy: The langcode key on configuration files is not explicit in configuration schema

Revert "Revert "Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code""

This reverts commit 079a52b4.

Revert "Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code"

This reverts commit 364a6e9c.

Issue #2457653 by Gábor Hojtsy: System.site langcode is both used as a file language code and a site language code

Issue #2170235 by Berdir, penyaskito, larowlan, alexpott, sushyl: file_private_path should be in $settings, like file_public_path

Issue #2379683 by Gábor Hojtsy: Fix configuration schema issues in contact (indirectly user and system) modules

Issue #474004 by mdrummond, kim.pepper, Wim Leers, jibran, tim.plunkett, joachim | JohnAlbin: Add options to system menu block so primary and secondary menus can be blocks rather than variables.

Issue #2301317 by pwolanin, dawehner, Wim Leers, effulgentsia, YesCT, xjm, alexpott: MenuLinkNG part4: Conversion.

Revert "Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion."

This reverts commit fd2db9cd.

Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion.

Issue #2256679 by alexpott, tim.plunkett: Fixed Use config schema to determine which config entity properties to export regardless of whether they are public or protected.

Issue #2283929 by tim.plunkett: Clean up condition plugins to have schema support and to allow them to be optional.

Issue #950534 by mparker17, mgifford, Mixologic, jbloomfield, erinclerico, theMusician, wmostrey | zirvap: [policy] Consistently use email instead of e-mail in Drupal.

Issue #2274175 by tim.plunkett, vijaycs85: Block plugin schema should be defined separately from the entity.

Issue #2259525 by alexpott: System.action.user_add_role_action.ROLE_ID does not match any config schema.

Issue #1399846 by slashrsm, Gábor Hojtsy, Berdir, brantwynn, visabhishek, David_Rothstein, cweagans, martin107, SteffenR, Dave Reid: Make unused file 'cleanup' configurable.

Issue #2218655 by sun, effulgentsia, jessebeach: Core expects $theme.settings default config file to exist.

Issue #2228921 by sun: Consolidate system.module + system.theme + system.theme.disabled into core.extension config.

Issue #2080823 by alexpott, swentel, Wim Leers: Create API to discover content or config entities' soft dependencies and use this to present a confirm form on module uninstall.

Issue #2167623 by danilenko_dn, sidharthap, Nitesh Sethia, krishnan.n, aitiba, alexpott, ashwinikumar, Barrett, damiankloip, deepakaryan1988, foxtrotcharlie, ianthomas_uk, neetu morwani, nonsie, piyuesh23, Sharique, sivaji, sushantpaste, swentel, vijaycs85, YesCT: Add test for all default configuration to ensure schema exists and is correct.

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 #2133325 by mtift, alexpott, sun: Create a site UUID on install and only allow config sync between sites with the same UUID.

Issue #2130811 by alexpott, Gábor Hojtsy, vijaycs85, sun, Wim Leers: Use config schema in saving and validating configuration form to ensure data is consistent and correct.

Issue #2098089 by penyaskito, Schnitzel, tim.plunkett, YesCT, EllaTheHarpy, Gábor Hojtsy: Fixed Date formats cannot be translated (the core UIs are useless).

Issue #2084339 by alexpott: Fixed The configuration value system.maintenance.enabled should be moved to the state system.

Issue #1934712 by dlu, alexpott, pplantinga, rbayliss, s_leu, Gaelan: Fixed Merge system.timezone config object into system.date.

Issue #2038285 by vijaycs85, Gábor Hojtsy: Update configuration schema for date formats as entities.