Add resize event and change hitbox on resize

This patch:
* Adds a resize event to "2D" triggered when h or w change
* Allow "Collision" hitboxes to track an entities shape through that event
* Change collision(polygon) to rotate the polygon before attaching it
* Fix some errors in calculating the MBR when a rotated entity was resized
* Adds some tests for resizing rotated objects
Merge pull request #485 from starwed/resize

Add resize event and change hitbox on resize