Issue #1891516 by sun, Berdir, chx: Remove $install parameter from DrupalUnitTestBase::enableModules(), encourage to create individual schema tables only.

Issue #1825466 by justafish, sun, alexpott: Allow NestedArray::mergeDeepArray() to preserve integer keys for the purpose of merging config data.

Issue #1788462 by samhassell: Remove references to 'active store' in comments for configuration system.

Issue #1666632 by sun, chx: Add Config::isNew() to allow code to determine whether a config object already exists.

Issue #1605324 by sun, Jose Reyero, alexpott, chx, Rob Loach | beejeebus: Configuration system cleanup and rearchitecture.