Some avatar specific change requests

I'd like to see the skin grain layers for the upper and lower body as separate textures rather than a reuse of the same texture.

It would be nice to have boxes for skin textures in the Appearance mode like the ones used for adding tattoos. Of course they would have to be layered below the tattoo textures.

Fix the nail polish layer so it sits below all the clothing layers (currently it sits above the undershirt layer), and fix the lower body freckle layer so it sits below the tattoo layers.

All these changes are backwards compatible with resident created products such as clothing and skins, so everyone would benefit from these changes.