Fixed transporting task with the OGDS Transporter between different admin_units.

The commits 9b75a9d and 910c829 brakes transporting tasks with the
`opengever.ogds.base.transporter.Transporter` from one admin unit to another.

I've added an tests for transporting tasks and refactored the `Transporter` object creation completely.
And dropped the no longer used interface `ogds.base.interfaces.IObjectCreator`.

@deiferni please have a look