Froide Version 4.0

- [x] Upgrade to Django 1.6
- [x] Upgrade dependencies
- [x] Upgrade to Boostrap 3.0
- [x] Replace User/Profile with Extended Custom User Model
- [x] Python 3 Support

Likely included
- [ ] Heroku deployment support
- [ ] Replace atomicity of slug generation
- [ ] Improve docs
- [ ] Attachment thumbnails