Persistent geometries

I implemented persistence for geometries. These can be store in db4o. Querying was described before this.

Each geometry has its own object's graph. During each update, this graph is updated. So some objects are created, updated or deleted.
For example, if user remove point from line string, object of this point is removed from database during update process and so on. Of course, transparently for users. User uses only store or delete on its geometries.

Tested for point, curves and multi-point. For testing surfaces, I have to implement operations overlay and relate. Other multi-geometries will be test later.