Improve width and height setter and getter
implementing Scene class
testing new width height scaleX scaleY AABB implementation
Basic implementation of width and height. Needs optimization and simplification
Optimizatin. AABB is kept up to date when getAABB() is called
1. Optimize AABB calculation, cache the lower and upper bound for merging.
2. Optimize local matrix calculation, only calculate matrix when necessary.
clean up
Future improvement, merge graphics' vertices