Evaluate tighter Sciebo/owncloud integration with a privately shared folder

[nuest]

Currently, we support loading from public owncloud shares via WebDav, so the user is the one making a connection between the services by copy and pasting a link (#1 in the figure below). To make this process simpler, we've created a "hack" within extender to extend the menus in the Sciebo UI (#2), instead of going into owncloud plugin development (#4 - we would have to run owncloud ourselves, get Sciebo to run it...).

A tighter integration would be to "join" a shared directory from an o2r service, because it would allow to stay "synced" (see #3).