Enhancement: Make notifications work with oCIS

Notifications now work when running oCIS as backend.

https://github.com/owncloud/web/pull/8518
https://github.com/owncloud/web/pull/8582
https://github.com/owncloud/web/pull/8595
https://github.com/owncloud/web/pull/8703
https://github.com/owncloud/web/issues/8519
https://github.com/owncloud/web/issues/8520
https://github.com/owncloud/web/issues/8593
