Separate internal BIH docs from SODAR manual

[mikkonie]

This is something which has been gnawing at me for a long time. The SODAR manual is a mishmash of 1) SODAR server software specific material, and 2) things only relevant to internal BIH, Charitë and MDC work. See e.g. #1745 for an example of the latter.

I have attempted to clarify in the docs that these two types of docs may co-inhabit the manual, but that's a temporary workaround at best.

SODAR has already been used in other organizations and there is little reason to believe this will not continue, so it would make to separate generic software and usage docs from stuff documenting internal processes.

How exactly to do this and how to maintain multiple documents? That is something we should discuss. I'm very much open for opinions.