Since  everything except the support of skins works now, let's talk about the skins again:

>At the moment, all skins use the same skeleton as far as I know. What this means in terms of appendto skeletons is that one file called "Clonk.appendto.skeleton" will append to the skeletons of all skins automatically, because their share the same skeleton.

>However, I would like to have the possibility that skins or also other extra graphics can have their own skeletons, and then one should be able to append to these skeletons as well.

So, in the future it should be possible, that the following files are in Clonk.ocd:
Clonk.skeleton,
Clonk.Farmer.skeleton

If there were only Clonk.skeleton, then appendto.Clonk.Farmer.skeleton would append to Clonk.skeleton.
If both files are present, then appendto.Clonk.Farmer.skeleton would append to Clonk.Farmer.skeleton?
Also, what should happen if appendto.Clonk.Farmer.skeleton and appendto.Clonk.Alchemist.skeleton both append to the same skeleton with the same animation name and different content/tracks?

I know that we just want to add appendto.Clonk.Farmer.skeleton to Clonk.skeleton at the moment, but these questions came up and maybe we can solve the, before I commit.

For the master branch my plan is the following:
Commit https://github.com/gitMarky/openclonk/commit/d32f66a43c7b5d0f3b21c31954374181670af8a9 separately
Commit the other commits on the learning branch squashed into one commit (including our solution for skins and remaining reviews)
Commit a restructured StdMeshSkeleton::MirrorAnimation