Test against python3
Update test-utils and django-nose.
Adapt code to python3

* Necessary code changes
* Update jingo version for py3 support
* Add python 3 classifiers
* Remove test_utils dependency of test suite since we're not using most of the features,
and keeping it as dependency will not help python 3 porting, we can do it.
Merge pull request #102 from coagulant/python3-round2

Python 3 support
Make core models abstract
Merge branch 'reattach'