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

Issue #2158571 by tstoeckler, dawehner, kgoel, tim.plunkett, catch, effulgentsia: Routes added in RouteSubscribers cannot be altered.

Issue #2098795 by tim.plunkett, Sean Charles, tstoeckler, dawehner, larowlan, damiankloip: Create Base Class for RouteSubscriber Class.

Issue #2091411 by damiankloip, dawehner: Provide an easier mechanism for a route definition wrapped by module_exists().