Add missing fields + generic relationship for pictures

The Picture model was wrong and now works as expected (generic).
Revert to django 1.7b1 while they fix this issue with migrations:
https://code.djangoproject.com/ticket/22485

Update serializers/bootstrapper with the new fields
Remove python 2.7 from Travis, because why not
Merge pull request #9 from Keats/connect

Add missing fields + generic relationship for pictures