Split the upper body

This splits the arms and hands from the torso into 4 separate groups. This started because of the silliness of the hand cutouts in the upper clothing — though this version does nothing about that specific issue. There's also been interest to make PortalCuffs, which would need individual visibility control over the arms and hands, as well as something Sepia also expressed interest in. So we joined forces and reusing the first unfinished pass at separating those limbs, finally ended at a place where this works.

Things changed by this:

• There's now 4 new groups: (Hands|Arms)(Left|Right).
• The Anklet and old Hands groups have been renamed and streamlined to follow the general $Limb$Side format, and to remove the duplicate with the new actual hands group. So those are now Anklet(Left|Right) and HandAccessory(Left|Right).

Things not changed by this:

• Do an overhaul pass of all the priorities. As it is, this works visually, but as the hands have been inserted into the stack to preserve the current behavior, there's no way to take advantage of the fact that they're now separated. That would be a prerequisite to removing the cutouts layers from most of the Cloth group.
• Another issue that doing this raised is the stupid placement of the hands in the OverTheHead pose. This pose singlehandedly caused all of the hands layer to be made size-specific, because the arms don't align to the same location. Fixing that would allow folding a lot of layers, but also a lot of tweaking over any asset that uses the OverTheHead pose to correct the arm's positioning.