Refactor specs

* use separate `describe` blocks for each method being tested
* improve language used to describe `it` blocks
* use full scope for `SimpleRepository` which allows spec file to be
  run separately
* put feature setup into a `before(:all)`
* put assertions from around main body of tests into `before` and
  `after` blocks
Support multiple features in Feature.run_with_activated
Support multiple features in Feature.run_with_deactivated
Merge pull request #22 from moneyadviceservice/multiple-features

Support testing with multiple features