Add "GameObjectProxy" which turns into a different GameObject based on an attribute value

[kb173]

Similar to ClusterGameObject, but instead of placing a varying number of other game objects, it only places one other game object. Which object that is, is decided based on a configurable attribute value or threshold.

Relevant for:

1. Automatically choosing onshore / offshore wind turbines
2. Allowing one brick color to place different objects based on the pop-up menu
3. Ability to have some smarter logic to choose e.g. which type of PV panel would make sense at a location