Fix for #22 and #218

#22: Updated to scrapper.py to return the cli options when the _MOZDOWNLOADARGCOMPLETE is in environment. Added completion scripts for bash and zsh. Updates to setup.py for the new completion scripts.
#218: Updated nightly with candidates in scrapper.py (ReleaseCandidateScrapper::candidate_build_list_regex). Updates to tests.
So what you want here is not to copy all the test files we have under the `nightly` subfolder, but only take those which are really appropriate for candidate builds. If you check the location on our FTP server where we actually download the candidate builds from, our local data folder needs an exact copy. It doesn't mean we need all the candidate builds, but a small set. Maybe only the candidate folder you can find under `nightly`.