Merge pull request #20719 from owncloud/adding-system-addressbook-of-users

apps/dav/appinfo/register_command.php

apps/dav/command/syncsystemaddressbook.php

apps/dav/lib/carddav/addressbook.php

apps/dav/lib/carddav/addressbookroot.php

apps/dav/lib/carddav/card.php

apps/dav/lib/carddav/carddavbackend.php

apps/dav/lib/carddav/converter.php

apps/dav/lib/carddav/plugin.php

apps/dav/lib/carddav/useraddressbooks.php

apps/dav/lib/dav/systemprincipalbackend.php

apps/dav/lib/rootcollection.php

apps/dav/lib/server.php

apps/dav/tests/travis/caldavtest/config/serverinfo.xml

...dav/tests/travis/caldavtest/tests/CardDAV/sync-report.xml

apps/dav/tests/unit/carddav/convertertest.php

apps/files_sharing/lib/helper.php

apps/files_sharing/settings-personal.php

lib/private/avatar.php

lib/private/user/manager.php

lib/private/user/user.php