Added Boolean isViewable() to Entity. The function just tells whether the
Entity is inside the GameBoard.viewable. Also Added void translateToScreen(Point)
to GameBoard. The function takes a point and translates it so it is relative to
GameBoard.viewable instead of the edge of the GameBoard.
Fixed bug of not taking into account the viewable's x and y position
Simplified some things
Simplified some more
added a particle system