Issue #2560641 by alexpott, lauriii, Xano, borisson_, ianthomas_uk: Remove all usages SafeMarkup::checkPlain() from render arrays

Issue #2505989 by alexpott, dawehner, olli: Controllers render caching at the top level and setting a custom page title lose the title on render cache hits

Issue #2076085 by dawehner, damiankloip, Letharion, pwolanin: Resolve the need for a 'title callback' using the route .

Issue #2032535 by dawehner, katbailey, pwolanin, Crell: Resolve 'title/title callback' by adding a _title propery on the route and allow a title be part of the render array.