Merge pull request #8540 from nextcloud/theming-advanced

apps/theming/appinfo/routes.php

apps/theming/css/settings-admin.css

apps/theming/css/settings-admin.scss

apps/theming/css/theming.scss

apps/theming/js/settings-admin.js

apps/theming/lib/Controller/IconController.php

apps/theming/lib/Controller/ThemingController.php

apps/theming/lib/ImageManager.php

apps/theming/lib/Settings/Admin.php

apps/theming/lib/ThemingDefaults.php

apps/theming/templates/settings-admin.php

apps/theming/tests/Controller/IconControllerTest.php

apps/theming/tests/Controller/ThemingControllerTest.php

apps/theming/tests/ImageManagerTest.php

apps/theming/tests/Settings/AdminTest.php

apps/theming/tests/ThemingDefaultsTest.php

lib/private/Server.php