Added extra clean option to run.py

BEWARE: Any local testing of this PR may have side effects on your current work, you've been warned!

This `-X` aka `--extra-clean` argument for `run.py` removes all the process files and folders, without rebuilding / recompiling them (unless combined with other arguments).

When combined with `-f` flushing (BEWARE as that flushes the local datastore), this extra clean option can show the project in a state that mirrors a fresh clone. With only the `./temp/` folder remaining, by design (see #105 for clarification).

Such a fresh state can help to compare projects a little easier, using for example KDiff3 to spot added/removed files and folders, and any changes. This can also be done with the process files in place, but they blur the view a little (and the list of places to ignore when comparing is getting longer).

Note that this (currently) also implements an assumption that the `main/static/src/vendor` and `main/static/vendor-fonts` folders can be wiped on an extra clean (similar to what is done in `Gruntfile.coffee` for the `bower` task... though that may never wipe the `vendor-fonts` folder?).