Add support for Django 1.10

[Geekfish]

This contains a few more changes and improvements than the title suggests:

• Cleanup tox config, add support for python 3.5.x. Remove duplication from tox.ini so that it's easier to set up additional environments.
• Add support for python 3.5 (tested on 3.5.1), but only for latest django versions (1.8.6+).
• Update manage.py to match latest django template.
• Add Django 1.10 to tox tests.

• Add support for --parallel flag for Django 1.9+. This required fixing how we get the total test count.

  When running tests in parallel, a core suite is generated to contain a collection of sub-suites that are then ran in parallel.

  In that case we have to go and retrieve the count from each of the sub-suites as the parent will not directly contain the tests.

• Remove redundant info from the README.

[hugorodgerbrown]

@Geekfish I've added you as a maintainer on PyPI - can you bump the version and push?