#16 reorganize examples

As proposed today and in https://limited.renku.ch/gitlab/sluis/aaad/-/issues/16#note_2509, I moved the toy problem "beam overlap" to examples and all other case studies temporarily to a to_clean_up subfolder - to decide what we keep as open-source examples, and removed all other locations.

We still need to clean up stuff from aaad/data @sluis - this folder should not exist anymore. (DATA constant already removed from repo with #25 (closed) and !22 (merged)).