Sanity tests, requirements, gitignore.

Hello, and thanks for the awesome admin tool.

I run a clone of this for redis backends [here](https://github.com/nicholasserra/django-redis-status). I recently added a __very simple__ sanity test structure and was thinking you might like it too. Basically just to catch Django changes causing issues. 

This PR includes:
* Test structure and a few sanity tests
* `requirements.txt`
* added blank `models.py` to make Django happy
* updated `.gitignore`

I also have a .travis.yml file to go along with this if you would like to enable travis tests across multiple Django versions. All you need to do is say the word and turn them on for this repo in your [Travis](https://travis-ci.org/) profile.

Thanks!