StarlingCamera - zoom and rotation needs to be explicitly allowed.

- first step to optimizing camera and porting StarlingCamera to
SpriteCamera.
- forcing users to allow rotation/zooming helps not doing unecessary
calculations for the camera's collisions with its bounds (such as
recreating non rotated/scaled AABB) if they are never going to use them.
- StarlingArt will no longer call pointFromLocal for every object,
camera will calculate camPosition once for each frame internally for
StarlingArt to use.
- moved rotatePoint to MathUtils