[bug 896137] Add django-badger

* add django-badger to vendor/
* add badger to INSTALLED_APPS
* add migration for django-badger related tables
* add django-badger strings extraction to settings.py

  Note that we only want specific .py files. We don't need to translate
  strings in the example or test code.
[bug 896137] Badges infrastructure

* adds kbadge django app which will centralize badge-related things
* adds notification for badge awarding which will email the awardee
* adds "award list", "award details" and "badge details" pages
* adds some really basic tests

At this point, you can:

1. create a badge in the admin
2. award a badge to someone in the admin
3. see the list of recently awarded badges (/badges/awards/)
4. see the details for a specific badge
   (/badges/badge/<badgeslug>/)
5. see the details for a specific award
   (/badges/badge/<badgeslug>/awards/<id>/)
Update migration-building-related docs