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.
I have removed #22 from the repository. So now the repository has changes only for #218. I am sending a pull request.

I did not got your comment for "git mv". These are new files added to the repository and not moved. I did copied them from the nightly using unix "cp -R" command and then using git add followed by git commit. What is that you want me to change in respect to #218.