Make the "Return to results" button point to results URL. Fixes #55

Originally, I used request.referrer, which is wrong because that just takes you back to the previous page. Now, the button points to session[:search_results] which holds the value of the search results URL, as defined in the controller.

Other changes in this commit:
- New integration test for the "Return to results" feature
- Refactor the integration test suite to move common methods in a helper module
- Improve the keyword and name search regex to use word boundaries (in the model scope)
- Create a second factory to be able to test the nearby feature