Smarter loading

A smarter, just in time loading mechanism speeds up the games initial loading tremendously (unless, of course you have a city with ALL the buildings in it ¯\_(ツ)_/. But if not, it really cuts down on the time to load the assets.

After you logged in, the buildings you have in your city will be loaded before they are displayed. Any other buildings are *not* loaded.

When you click on a structure icon, the building is loaded and cached.

![image](https://f.cloud.github.com/assets/985892/2251094/86799e96-9d98-11e3-91dd-e9303d6a97b3.png)


ref #124, #8