add ability to change hue / saturation of a layer by keyframe

[genestrashcan]

add the ability to change hue/saturation of a layer by keyframe.

I am creating a video where a Naga girl (think medusa) gives a girl a "Snake Massage" and I want to adjust hue/saturation by keyframe to have the girl's face turn slightly red during each "coil squeeze"

[p-yukusai]

Added HSV keys for layer nodes, pending merge.