Add in new query class called Querist

http://www.oxforddictionaries.com/definition/english/querist
Add request promise

- wrap up general request logic in request-promise
- add in chai-as-promised to check our promises
Add require-subvert

Allows us to mock dependencies that are required on a function that is exported on a module.
Add lots of tests for request-promise
Fixed up testing for querist

Use require-subvert to test the exported function
Updated look of test to make it a little more readable
set node_env inside to fix build issues
q
Merge pull request #14 from alphagov/datasets

Adding query class