Drop Django 1.3 and add Django trunk support

- Drop Django 1.3 from test environments
- Fix imports to work with Django trunk

Branch: django-upgrade
Start RapidSMS 0.12.0 release notes
Drop Django 1.3 from Travis too; test against latest Django 1.4.5
Branch: django-upgrade
Merge branch 'django-upgrade' into release-0.12.0