Isolate game-specific code from engine-specific code.

[lukaspj]

Why is the Models.Base folder in the game code project? Surely, this folder reflects the engine structure, and therefore it should be in the Winterleaf.Engine project.

Also whats the purpose of the "Extendable" folder, it seems like it isn't meant to be fiddled with just like the Models.Base folder, so whats its purpose? What does it add that you couldn't just get from the Models.Base classes to begin with? Edit: Nvm, I see it's for inheritance

Winterleaf.Demo.Full should just have "CustomObjects" and "GameCode".