Combine the `rizmu` and `develop` branches - fixes Django 1.9 support

[vdboor]

This pull request combines both of external branches that fix Django 1.9 support.

The rizmu branch has the most features, while the develop has other fixes. In turn this hurts Django 1.9 projects: one branch has the mimetype -> content_type fix, the other has the importlib fix. both are needed for Django 1.9. I've also updated the urls.py for Django 1.10