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.
A better way to implement this spec would be to:

```
subject { build_stubbed(:sponsor_type) }

it 'should be valid with all the correct attributes' do
   expect(subject).to be_valid
end

it 'should be invalid without code' do
  expect(build_stubbed(:sponsor_type, code: '')).to_not be_valid
end

it 'should be invalid without unique name' do
  sponsor_type = create(:sponsor_type)
  expect(build_stubbed(:sponsor_type, name: sponsor_type.name)).to_not be_valid
end

...
```