Add Color Temperature on lights

[JenusL]

Arnold Light has Temperature controls in at least 3ds Max, Maya and Cinema 4D. We should add those to Softimage as well.
I've been going through the code in MtoA and it's very basic and (I think) it doesn't take into account the rendering colorspace defined in color managers.
I would like to implement it properly in SItoA:

• Temperature slider in Kelvin
• ±Green slider, mimics green/magenta gels on real lights. This is necessary to have on a light for proper color matching.
• Drop-down list with industry standard presets.
• Implementation should query AiColorManagerGetChromaticities() to properly convert the XYZ color to the correct rendering color.

I hope in the future that Arnold Cameras also will include a color parameter. This should be implemented with that in mind so that when the day comes the code can just be applied on cameras as well.

[JenusL]

Now that Arnold 6.1 has white balance capabilities, it make sense to implement this.