Added Scale3Bitmap and Scale9Bitmap display objects

Scale3Bitmap: Supports three regions, for a pill-shaped scaling bitmap. Can be horizontal or vertical. Center region stretches in both directions to fill available space. If outer regions are scaled, they will maintain aspect ratio.

Scale9Bitmap: Supports nine regions, similar to scale9Grid that is available to Flash display objects.

In both cases, scaling can be controlled by setting drawWidth and drawHeight or by calling setDrawSize(). These values will default to the width and height of the image that is passed into the constructor. I chose these names to avoid conflicts that may arise if EaselJS ever adds width, height, or setSize().