Show "limbs" bones belong to, add an option to group bones in a single limb

[Nico-Duduf]

when a chain of bones is created, it is assigned an id which makes it a limb, and the duplication tool takes care of that. But if you manually add a bone, it is not considered to be part of the limb and has another id, so the autorig and OCO won't work correctly
But there's something to improve in Duik with this. There should be some way to visually show these limbs and be able to reassign bones to limbs, a bit like groups

I think bone colors can help, I may add a button like 'show limbs' which would turn the color of the bones according to the limb they belong to; along with another simple button 'group selected bones in limb', something like that