Merge pull request #13621 from owncloud/system-config-multiset

core/command/db/converttype.php

lib/private/allconfig.php

lib/private/config.php

lib/private/legacy/config.php

lib/private/setup.php

lib/private/setup/abstractdatabase.php

lib/private/setup/mssql.php

lib/private/setup/mysql.php

lib/private/setup/oci.php

lib/private/setup/postgresql.php

lib/private/systemconfig.php

lib/public/iconfig.php

settings/controller/mailsettingscontroller.php

tests/lib/config.php

tests/settings/controller/mailsettingscontrollertest.php