Order number + Lightbox tabs fix

This resolves the issue where commodities (or declarable headings) failed to render due to presence of order numbers without descriptions. We didn't pass pass casted_by when initializing such order number and it was expected by OrderNumber#id.

See https://github.com/alphagov/trade-tariff-frontend/pull/new/lightbox-tabs-fix#L6L78.

Also, invoking a lightbox changes your URL so that lightbox is uniquely identified and the user can pass this link to somebody else. Closing lightbox changes the link back to #import or #export. The only issue is that the user who receives and opens such a link will see the lightbox in question but will have his URL instantly changed to #import or #export. This is a limitation of tabs plugin we are using https://github.com/alphagov/static/blob/master/app/assets/javascripts/jquery.tabs.js. This is not a particularly good behaviour in this case, but changing this requires some heavy tabs plugin modification and I believe it should come as a separate story. Btw, the plugin does not seem to be easily extendable.