Miscellaneous fixes

This MR contains a group of unrelated commits that fixes some issues. The "most important" changes are:

• When a picture is saved, it was saved into .pdf and .svg. I changed .svg back to .png because .svg does not work well with PowerPoint.
• I added a processing edges_at_least_3_planes just after the embedding, which allows to consider that a track is genuine only if it has 3 hits on 3 different planes.