Add BlendComposite.java

The class is adapted from a demo tool for Blending Modes written by
Romain Guy (romainguy@android.com). The tool is available at
http://www.curious-creature.org/2006/09/20/new-blendings-modes-for-java2d/

Change-Id: I8f7c7ca08d3078106056764a4e2f1ce95d990137