Improve dev-dependency-removing UX

[gnunicorn]

To prevent dependency-cycles multiple commands currently by default remove dev-dependencies from the Cargo.toml-files first. While neat, the UX is still lacking because:

• if you change specific files an then run the command, you can't just commit what you had before, because the files were edited
• if the command fails, you have to revert all chagnes and do your local changes again, as it is pretty hard to figure out what had changed

Let's do the following:

1. create a .Cargo.toml.backup when we remove the dev-deps
2. only create that file when we actually removed dev-deps
3. add another command to quickly revert-de-dev-dep copying back the backup files. allowing to jump back to the state before
4. maybe automatically run that revert if the patching-command failed?