Only fragments roots are handled correctly when objects are moved

[markus1978]

When an object gets a new container its id index entry has to be updated and it also has to move from one UOC to another. But it looks like this is only done for objects that are root or become root of a fragment. However, this is not thoroughly tested.

This related to:

1. Incremental remove #12
2. Incremental reference updates #13
3. Deletion of objects with extrinsic ID #14

[markus1978]

When objects are moved, also their contents has to be moved with respect to the UOCs and IDs, see also #13.

[markus1978]

Removing a user object from one UOC and adding a new user object to another UOC is not really moving.

[markus1978]

Resolved, but not for multiple models. Incremental remove #12, #14 still a problem.