Plan & structure source tree

with more and more code arriving, we should probably think about (and implement) a source tree structure. This concerns both repo layout but also which code lands in which library.

• have central components centrally
• do we want to separate "our" satellites vs "user" satellites that might land?
• do we want to add user satellites at all into the repo?
• should this repo move to gh eventually to allow r/w access for anyone with an account?
• ...