django 1.7

This pull request is only here for the compatibility of our code with Django 1.7. I don't want to change (or think about a change) of an app. The way I used is the direct upgrade from the old behaviour. The "problem", that there could be fields in the model that should not be in the form has also before.

I am also a bit surprised that you have a problem with fields = '\__all\__', because normally you were a fan of the possibility to automatically generate the form.