Merge pull request #14468 from owncloud/af-db-cleanup

lib/private/appframework/db/db.php

lib/private/server.php

lib/private/tagging/tagmapper.php

lib/public/appframework/db/mapper.php

lib/public/idb.php

lib/public/idbconnection.php

lib/public/iservercontainer.php

tests/lib/appframework/db/mappertest.php

tests/lib/appframework/db/mappertestutility.php

tests/lib/tags.php