Changes:
* add .DS_Store to .gitignore
* Decode base64 encoded emails for tests
* Pick a version of scikit since the pickled clasifiers are based on that
* Add missing numpy and scipy dependencies
I never was actually able to successfully install PyML but the source-forge
distribution and lack of python3 support convinced me that scikit-learn would
be a fine substitute. Flanker was also difficult for me to install and seemed
only to be used in the tests, so I removed it as well to get into a position
where I could run the tests. As of this commit, only one is not passing
(test_standard_replies with android.eml) though I'm not familiar with the `email`
library yet.
