Documentation game.model

Documentation for:
* game.model.Door
* game.model.Entity
* game.model.Position
* game.model.SpotAnimation
* game.model.shop.GeneralStore
* game.model.shop.Shop
* game.model.shop.StockType
* game.model.shop.StockedShop

Format
* game.model.player.ShopHandler (I moved an if statement as well :P).