Modernize much of the code in rb-extension-pack.
Review Request #5532 — Created Feb. 23, 2014 and submitted
Most of the extensions weren't compatible with Django 1.6, due to legacy
imports. I've fixed those, updated the extensions to use
initialize()instead of__init__(), and removed some bad practices
(like assigning a hook to a variable on the extension, which wasn't
necessary or even a good idea).
Enabled each of the extensions.
