Improve i18n a bit.

I'm working on integrating the Italian localization that we recieved at
https://reviews.reviewboard.org/r/4298/

There are a few things that were getting in the way here. We have some old i18n
scripts in contrib/ which mostly work, but should be removed in favor of the
django-admin.py versions. The django-admin.py version of makemessages was
erroring out in a couple places where we were using positional format strings
with multiple arguments, instead of parameter names. I've fixed these up.

There are also several strings which aren't marked for translation. A lot of
these are likely coming from javascript, but one that was immediately obvious
was the dashboard's sidebar.

Integrated the contributed Italian localization files, and ran
compilemessages. Set my browser to prefer Italian, and saw that most of
the UI was now translated. Neat.