Add logic to controller to handle new pricing format

There is a new format for the Pricing question. This update to the controller saves the new fields properly.
Use same key for all pricing inputs
Attach question 1 errors to same key

Question 1 has several parts but validation error messages should be attached to the question as a whole, not to the individual parts.
Match the keys for errors to the content
Merge pull request #71 from alphagov/pricing_controller

Add logic to controller to handle new pricing format