Updated to support the latest Django and Python versions

[Ecno92]

I've updated the project to match the current supported Django versions and their supported Python versions.

Also I have applied minor improvement including:

• fixing the version of tox-travis to avoid issues with backwards incompatible version upgrades
• Changed the development status from beta to production as I know it has been running in production setups with good results.
• Fixed the setuptools version. If you install python using pyenv you get the wrong setuptools version by default and this makes the installation crash.
• fixed some linting issues in the travis file

I hope that I touched everything that is relevant for this upgrade.

Also notice that users do not need to upgrade. The non-testing code of this project did not change.

[coveralls]

Coverage increased (+0.03%) to 96.429% when pulling 48c2f59 on Ecno92:feature-latest-django-support into b7951be on pennersr:master.

[coveralls]

Coverage increased (+0.03%) to 96.429% when pulling 8264131 on Ecno92:feature-latest-django-support into b7951be on pennersr:master.