Update to 'shoulda-context' v1.2.1

The test changes are necessary because defining scoped methods within
the "context" blocks doesn't work anymore.

The bump is done so that it's possible to use the latest release of 'shoulda'
which pulls in the 'shoulda-context' gem.
Add 'shoulda', make validation tests more concise
Need test refinements

- move validation tests into separate context block for clarity
- add explicit setup blocks to context blocks to make dependencies more obvious
Add FactoryGirl syntactic sugar

This makes the create statements shorter
Use factory_girl more for creating models in NeedTest
Merge pull request #71 from alphagov/use-shoulda-for-more-concise-tests

Use 'shoulda' for more concise tests