Support 3.7, re-target Django supported versions, tox updates.

[urda]

CHANGELOG includes:

TODO: RE-ADD CHANGELOG AFTER REBASE

[urda]

This PR needs some adjustments to allign with the following (excluding Python 2 as support was dropped long ago for this project):

Source: https://www.djangoproject.com/download/#supported-versions

Source: https://docs.djangoproject.com/en/2.1/faq/install/#what-python-version-can-i-use-with-django

[codecov[bot]]

Codecov Report

Merging #82 into develop will not change coverage. The diff coverage is n/a.

@@          Coverage Diff           @@
##           develop    #82   +/-   ##
======================================
  Coverage      100%   100%           
======================================
  Files            3      3           
  Lines           23     23           
======================================
  Hits            23     23

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update be9e286...de16f92. Read the comment docs.

[urda]

Cross checking versions and the diff again, planning to merge to develop at least.

[urda]

I'm planning on breaking this PR up into a few parts:

• Raw Django version upgrades without any 3.4 or 3.7 changes.
  • Which would include adjustments for skipping 3.4 during testing of 2.1 and later 2.2.
• Support for Python 3.7

All of which will have README values. Closing this PR in favor of those (future) PRs. Will be linked back here.

[urda]

Spawned a PR #83

[urda]

Spawned a PR #84

[urda]

Spawned a PR #85