Cleanup the documentation

[MakisH]

I went through all the documentation and improved a bit the structure, the language, and removed some outdated content.

This PR is accompanied by this PR on the website: precice/precice.github.io#962

Summary:

• Removed the very outdated page on building on SuperMUC - a system that does not exist anymore, and with comments that do not add much value on any other situation nowadays, especially since we no longer depend on yaml-cpp.
• Since the documentation was moved from the website repository to this repository, depending on variables for the CalculiX and adapter versions that are defined in the website repository is strange and make the documentation confusing when viewed locally. I replaced these variables with hard-coded values, which anyway need to be updated together with the rest of the content when changing versions.
• For the configure.md, I moved some sections around to make the page easier to follow, and fixed several language and other minor issues.

This PR will conflict with #146, so I am waiting to get that one merged first and handle the conflicts here.