This property can be queries by the clients so they know the max
permissions they can use to share a file with. This will improve the UX.
The oc:permissions proptery is not enough since mountpoints have
different permissions (delete + move by default).
By making it a new property the clients can just request it. On older
servers it will just return a 404 for that property (and thus they know
they have to fall back to their hacky work arounds). But if the property
is returned the client can show proper info.
* unit tests
* intergration test
Introduce a new property "oc:fileid" to return the internal file id.
This is because the original "oc:id" property is a compound and it is
not possible to extract the real id without knowing the instance id. The
instance id is not available to external clients.
