LIGHT phase - new deviance options + sRGB lightmaps support

-new -lightmapsrgb arg generates sRGB lightmaps in PNG format (vertex
light are keeped linear)
-new -nosrgb arg forces linear lightmaps
-new -deviancesamplesscale arg scales number of deviance lights
-new -devianceform arg set form of random distribution (0 - box, 1 -
sphere)
-new -devianceatten arg set attenuation for random distribution (0 - no
atten, 1 - inverse square falloff)
- ColorToBytes slightly optimized (breaked into the functions avoiding
if()'s)
- "lightmapsRGB" key now set on worldspawn to indicate whether lightmaps
is sRGB or not (but with PNG this is not nesessary, as PNG's are checked
by ICC profile)