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.
building on @sampritipanda's example, an alternative solution (which I use a lot myself):

```ruby
subject { build_stubbed(:sponsor_type, attributes) }

let(:attributes) { Hash.new }

it 'should be valid with all the correct attributes' do
   expect(subject).to be_valid
end

context 'with an invalid code' do
  let(:attributes) { sponsor_type_code: '' }

  it { is_expected.not_to be_valid }
end

context 'without a unique name' do
  let(:existing_sponsor_type) { create(:sponsor_type) }
  let(:attributes) { existing_sponsor_type.name }

  it { is_expected.not_to be_valid }
end

...
```