Update requirements

Work toward Symposion managing its own dependencies:

* Created a requirements file
* Added these requirements to `setup.py` installation
* Updated the quickstart instructions in the README

I also removed fixture_gen files that require [django-fixture-generator](https://github.com/alex/django-fixture-generator), which has not been updated since Django 1.2, and a test file which does not run since Symposion updated its project structure.