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.
@sampritipanda, @yggie
Bryan, it seems to me that our approaches are identical, but with different syntax: Create a valid object first, then iteratively invalidate its attributes and test that the object becomes invalid as the result. Is the syntax difference critical or rather a matter of style?

Sampriti, after some experimenting and reading, I see that my earlier comment was incorrect: explicitly defining `subject` makes it the receiver for all `should(_not)`, including those in `context` blocks.

The `should` syntax is used because `it { is_expected.to }` is not supported by RSpec 2.14, which we use currently. We have PR #14 to upgrade to RSpec 3.0.