Reorganize CAD files
@mikelovic has already moved the CAD files to the CAD
directory in commit 0348e6d0. Currently this doesn't match well with @Johannes-Hoelzel work that makes it difficult to merge his contributions. I propose to revert the CAD file change and defer the decision to reorganize the repository if we have a clear understanding of what directory structure we want. At least I am not yet aware of a definite solution for the directory structure as discussed in this issue.