Local Git archiving and Zenodo support

* Implemented support for Zenodo. Currently this only works when publishing software, not data.
* Zip up the local Git repository using the 'git archive' functionality, so that PyRDM is not restricted to repositories hosted on GitHub. Note that if this fails, PyRDM will fall back to trying to download the archive from GitHub as a last resort.
* Use argparse rather than optparse.
* Renamed article_id to pid (publication ID), except in figshare.py to maintain consistency with the current Figshare API documentation, since the use of the word 'article' can get confusing when talking about publishing code.
* Started work on Bazaar VCS support.