added class Camera
added camera to game
made camera static
many things now use camera position
added arguments to update of clickables
clickables now work as previously
tower placing now works more or less
Tower placing now works like before
placing other towers correct now, too
healthbars and enemy radius now rendered at correct position
debug things now rendered at correct positions
restructuring
projectiles now rendered at correct positions
added methods addX and addY
camera now controlled by keys
hinder camera from moving too far to the left
keep camera from moving up, outside the frame
keep camera from moving too far right
keep camera from moving too far down
checks now should also work with zoomed view