added GameEnd event to GameController

changed occurences of ifs on the gameEnded variable with listenting to
the GameEnd event and disabling the component.
refactored Building

added Levelable, Damagable and Polluting component. Used building models
(GameObjects) for the different levels as children of the building Game
Object
Changed particle effects on some buildings to come directly out of the
chimney.
refactored tree component

added levelable, damagabel and polluting (negative) component.