Move admin sections to settings app

apps/settings/appinfo/info.xml

apps/settings/composer/composer/autoload_classmap.php

apps/settings/composer/composer/autoload_static.php

apps/settings/lib/Sections/Admin/Additional.php

apps/settings/lib/Sections/Admin/Groupware.php

apps/settings/lib/Sections/Admin/Overview.php

apps/settings/lib/Sections/Admin/Security.php

apps/settings/lib/Sections/Admin/Server.php

apps/settings/lib/Sections/Admin/Sharing.php

lib/private/Settings/Manager.php

tests/lib/Settings/ManagerTest.php