Migrate logic to dynamic controller

apps/theming/appinfo/app.php

apps/theming/appinfo/info.xml

apps/theming/appinfo/routes.php

apps/theming/js/settings-admin.js

apps/theming/lib/controller/themingcontroller.php

apps/theming/lib/init.php

apps/theming/lib/template.php

apps/theming/settings/settings-admin.php

apps/theming/templates/settings-admin.php

apps/theming/tests/lib/TemplateTest.php

apps/theming/tests/lib/controller/ThemingControllerTest.php

core/js/config.php

core/shipped.json

lib/private/Server.php

lib/private/legacy/defaults.php

lib/private/legacy/template.php