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

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