Summary:
Implement DAV folder sharing based on draft-pot-webdav-resource-sharing standard
We keep the DAV ACL standard implementation as an option, but this standard
does not cover the folder discovery, so we'll not use it with Kolab setups.
Reviewers: #roundcube_kolab_plugins_developers
Subscribers: #roundcube_kolab_plugins_developers
Differential Revision: https://git.kolab.org/D4668
