Add attractiveness filter

Some other changes that I made that are worth mentioning
- settings.py now looks in the environment for credentials
- the Session object has a login method
- Search requests are now gets rather than posts (as they should be)
- I got rid of the headers that were being sent with login because they don't appear to be necessary
- Add location instance variable to user, use that location as default for search.
- Move pyokc.py to user.py
- Make search, User and AttractivenessFinder available as direct imports