Blender Git Loki

Fixes to Color Balance node:

* The Lift/Gamma/Gain formula previously was incorrect, fixed this and
removed conversions - now the RNA values are the same as what goes into
the formula.
* Because of this, added the ability for the Value slider to map to a wider range
than 0.0-1.0. The black/white gradient remains the same, in this case just
indicating darker/brighter rather than absolute colour values. Also added ability
for color wheels to be locked at full brightness (useful for this case, where the
color value itself is dark).
* Added an alternate formula - offset/power/slope (asc-cdl). This fits the standard
Color Decision List formula, here for compatibility with other systems, though
default Lift/Gamma/Gain is easier to use and gives nicer results.