Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

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

Issue #2444231 by Wim Leers, nlisgo: Fix CacheableInterface so it makes sense (was: "Make Config objects & Entities implement CacheableInterface + add BubbleableMetadata::createFromCacheableObject()")

Issue #2271251 by ParisLiakos, undertext, JeroenT, StevenPatz, tim.plunkett: Remove usages of watchdog() from non-form and non-controllers.

Issue #2222719 by effulgentsia, tim.plunkett, xjm, dawehner: Use parameter matching via reflection for access checks instead of pulling variables from request attributes.

Issue #2109035 by tim.plunkett, damiankloip, dawehner, chx: Make access checkers (much) easier to find.

Issue #2048223 by dawehner, ParisLiakos, herom, fubhy, damiankloip, vijaycs85, joelpittet, tim.plunkett: Add $account argument to AccessCheckInterface::access() method and use the current_user() service.

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

Issue #2063405 by dawehner, Wim Leers, Crell: Update all access checkers to use static::ALLOW/static::DENY/static::KILL.

Issue #1793520 by disasm, klausi, tnightingale, Crell: Add access control mechanism for new router system.