I've put it temporarily in the Draft Workbench, src/Mod/Draft, just because I am refactoring commands with a certain style.
So the notch command is three files, a function to create it and an object class in draftobjects/, a GUI command in draftguitools/, and a view provider in draftviewproviders/.
I think this tool makes more sense in some sort of assembly workbench, or woodworking workbench.
I also don't quite understand why it creates two NotchConnector objects. I didn't test enough, I just wanted to test the structure by placing different parts of the code in different directories.