Clarify entity position interpretation

If the scenario engines or other modules in the environment use the IEntity->Set/GetPosition() functions, they have to make an assumption what the reference position of the entity is in the MantleAPI:

• the origin of the coordinate system of the entity
• the geometric center of the bounding box of the entity

In the OpenPASS meeting on 17th of February 2022 we discussed this and came to the conclusion that the geometric center of the bounding box shall be used as position.