Optimize compositing of the shader

Change-Id: I76a7c4a51668e92a86b948f85545ee68381f8287
Updated baseline image

Verified using the FixedPointVolumeRayCastMapper that
new mapper image is closes vs the old mapper which didn't
consider the ambient component correctly

Change-Id: I2e4da78cd855ce80f368dcc51b8cef57bb57416e
Updated baseline for lightkit test

Change-Id: I91b3f4b40cc53a162fb6419f9390820b7b57bbf9
Tweaked few lighting parameters

Change-Id: I69f72edad3ad0dafba4122735d5bfabfe2ec849e