support for loading images using transform options
ColorTransform

Load images using ColorTransform parameters (including also a non
default NONE value). Used to load images
from file / buffer.
Introduce BitmapData file / namespace for future development
fixed BlendMode.NONE with straight alpha
BitmapData.setTransparentColor

- added BitmapData.premultiplyAlpha()
- added BitmapData.setTransparentColor()
- added ColorTransform. TRANSPARENT_BLACK
- added ColorTransform. TRANSPARENT_WHITE