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.
since you assigned the subject as the `sponsor_type`, this let block is redundant, the same effect can be achieved with: `subject { build_stubbed(:sponsor_type) }`