Correctly support pre-multiplied alpha, optimizations, more stuff.

Add support for the following drawing functions:
- drawBitmap(int[]...)
- drawPaint()

Optimizes shader state changes by enabling/disabling attribute arrays
only when needed.

Adds quick rejects when drawing trivial shapes to avoid unnecessary
OpenGL operations.

Change-Id: Ic2c6c2ed1523d08a63a8c95601a1ec40b6c7fbc9