3497: minor refactoring of will it work for me controller
3497: minor refactoring of will it work for me controller

Make the code a bit easier to read by splitting out the part that
determines the next URI

Authors: f2c387db31f41310970101df13c597dac7f1f09e@leoshaw

alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend