Problem/Motivation
As seen on #1974408: Convert aggregator_page_source() to a Controller, routes defined via the route system does not have yet the concept of titles. Titles
are not only needed for menu links, but also for the actual title on the page, so things which has been MENU_CALLBACK's before also have titles.
Proposed resolution
TODO
Remaining tasks
API changes
Related Issues
#1974408: Convert aggregator_page_source() to a Controller
#1889790: [Meta] Allow modules to register links for menus, breadcrumbs and tabs (if not with hook_menu)
#1830588: Put the page title on the page array (or its replacement), remove drupal_set_title()
#1839338: [meta] Remove drupal_set_*() drupal_add_*() in favour of #attached/response for out-of-band stuff
#2023795: REGRESSION: hook_local_actions doesn't use title callback
#2027183: hook_menu() title callback is ignored on routes
#2031473: Convert menu local actions to plugins so that we can generate dynamic titles and paths