Change storage (wood) to be a float behind scenes

[jellewie]

Change the wood stone money etc to be a float behind the scene. This would enable to get a return on cheap buildings. Like the wooden wall is 1 wood and would then terurn 0.5 for example (wich would not be shown, math round down) but when you remove another wall of 0.5 you will get a wood back.

This could also enable us to ask less wood per wooden wall if it's lower than normal