Generic building system

[Thaoh]

It should allow us to:

1. Select a building from a menu of some sort
2. Select where to build it
3. Check if you have enough resources to build the building.
   a. if you do not have enough resources, display a red transparent model of the building in the correct plot you are hovering over
   b. If you do have enough resources, display a green transparent model of the building in the correct plot you are hovering over
4. build the building if you are able to, and click on an open spot