Merge pull request #10107 from owncloud/sharing_group_shares

apps/files_sharing/appinfo/app.php

apps/files_sharing/lib/exceptions.php

apps/files_sharing/lib/share/file.php

apps/files_sharing/lib/sharedmount.php

apps/files_sharing/lib/sharedstorage.php

apps/files_sharing/tests/base.php

apps/files_sharing/tests/share.php

apps/files_sharing/tests/sharedmount.php

lib/private/share/helper.php

lib/private/share/hooks.php

lib/private/share/share.php

lib/public/share.php

tests/lib/share/backend.php

tests/lib/share/share.php