Add additional integrations for Django and command-line usage of unittest

This commit adds some easy usage shortcuts for Django (see #23) and also provides the ability to run unittests from the command line (normally `python -m unittest`) using the `TeamcityTestRunner` instead (usage: `python -m teamcity.unittestpy`).

For Django support, add in the settings.py: `TEST_RUNNER = "teamcity.django.TeamcityDjangoRunner"`

I didn't add tests for this, as it is hardly testable at all and including Django entirely in the requirements seems a bit overkill.