Implement factory girl

Pivotal Tracker story Switch to FactoryGirl: https://www.pivotaltracker.com/story/show/75757844.
- add factory_girl_rails gem
- create factories for partners, provinces, sponsor_types, sponsors, statuses
- create model spec for sponsor_type using sponsor_types factory

All factories confirmed to create valid objects.
David Chelimsky calls explicit use of 'subject' a [spec smell](http://blog.davidchelimsky.net/blog/2012/05/13/spec-smell-explicit-use-of-subject/), but allows a few exceptions. My usage is one of those exceptions. His argument, with which I agree, is that `subject.name` is obscure. Using a named subject helps to understand the spec's intention quicker.