Consider moving from vcsh to yadm

[ThomasFeher]

https://thelocehiliosan.github.io/yadm/

improvements:

• "yadm makes it possible to use alternate versions of files based on the OS or hostname of the system"
• bootstrapping (you can provide a script, that is executed automatically when installing the configuration the first time). See example on how to install all vim plugins
• conflicting files are overridden automatically and the old files are stored as git-stash
• handles submodules correctly

downsides:

• only one repository (not really an issue, because I'm using only one repository currently)