Entity.add_property() with an id matching a special attribute should set the special attribute
Follow-up to #217.
The behaviour described in that issue should also be implemented for method calls using id, e.g. id=20 for name. Some questions that need to be clarified beforehand:
- Would it be save to assume/hardcode the special attribute ids, or are they subject to change
- If not, how are they accessible? Cache?
- How to deal with instances where id and name do not match, e.g. id=20 but name=TestProp