Improve OrderNumber handling.

It is represented by single hash instead of ordernumber: "" and
order_number: {}.
Correctly identify OrderNumber Definition presence.
Move around fields, add improve usability.
Merge pull request #50 from alphagov/search_form_improvements

Move around fields, add improve usability.
Merge pull request #49 from alphagov/quota_order_number_refactor

Quota order number refactor