Add renderscript blur

Implements a new BlurProcess that uses Renderscript's Intrinsic Blur
Filter to blur quickly
Update example app to support renderscript
Use the renderscript support library

The renderscript support library works back to android 2.2, instead of
only 4.2 and above.
It does not currently support ARM before v7a, and will fallback to the
NDK rendering if it cannot use renderscript
Support alpha preservation when blurring with renderscript

This just copies the alpha of the original image onto the blurred copy.