Merge pull request #16368 from owncloud/occ-config-commands

core/command/base.php

core/command/config/app/deleteconfig.php

core/command/config/app/getconfig.php

core/command/config/app/setconfig.php

core/command/config/import.php

core/command/config/listconfigs.php

core/command/config/system/deleteconfig.php

core/command/config/system/getconfig.php

core/command/config/system/setconfig.php

core/register_command.php

issue_template.md

lib/private/systemconfig.php

tests/core/command/config/app/deleteconfigtest.php

tests/core/command/config/app/getconfigtest.php

tests/core/command/config/app/setconfigtest.php

tests/core/command/config/importtest.php

tests/core/command/config/listconfigstest.php

tests/core/command/config/system/deleteconfigtest.php

tests/core/command/config/system/getconfigtest.php

tests/core/command/config/system/setconfigtest.php