Multiple settings separation

Hi there, I thought it would be easier for other people to contribute if the settings are clearly separated
and if it's more explicit to choose if you're working on `local`, `production` or just running the `test`.

So I've done 3 separated `settings`:
* base ( common for every case)
* local (for local development)
* production (with heroku + aws, etc...)

And to keep it consistent I've separated the requirements.txt into 4:

* base
* local (ex: sphinx)
* production (with gunicorn and etc..)
* tests (with factory-boy)

also I've update the `README.markdown` to reflect this changes, 
and also added the lines for loading the fixtures for django 1.4..1.7 that were missing.

I've run it locally and everything seems to be fine, the tests are running ok, and also pushed to my heroku to check it on production.

Hope this'll help out newcomers =)