ref #23 - Upgrade django-chartjs to python35 and Django 1.8+

[FlogFr]

Upgrade support to python 2.7 + 3.4 + 3.5, on Django 1.8 + 1.9 and 1.10

ref #23

• [x] change tox.ini
• [x] change .travis.yml
• [x] update demoproject and settings in order to unit tests to pass
• [ ] need to do a new release or release on PyPi for python3 ?

[FlogFr]

Should we release a new version or same version under universal wheel for py2 and py3?

[Natim]

A new version :)

[FlogFr]

PR ready for review

[Natim]

Yes I guess it is good if people can run the same things as travis does locally using tox

[FlogFr]

Updated to have the matrice in tox :)