renamed IEntityListener to IActorListener to match the renaming Entity
-> Actor
created basic projectiles and first subclasses for Nitro's SMG (fired
with primary action button from stub-position)
prepended some class-variables with underscore to match
coding-guidelines
the game itself now fires a render-event (onRender) when the game is
re-drawn -> IGameListeners have to implement this method (done for all
current IGameListeners)
images for bullets are not static to have only one instance per image.
Should probably be applied to other renderers as well?