Clean up documentation structure

As discussed in the requirement refinement meeting on the documentation structure on 08.09.2021, the sections "User Guides/Simulator" and "Advanced Topics/Simulator" are currently not easily differentiable. Therefore, a clear distinction has to be made using according wording and the documentation has to be updated accordingly. This is i.e. relevant for different sorts of openPASS components.

A solution will have to be discussed within the AC first of all.