Enhance goods code not being found handling code

Adds some intelligent redirects based on search in the API. E.g.:

* If you try to reach non existing sections redirects to sections listing.
* If you type a wrong heading ID tries to redirect you to a relevant chapter.
* If you access a commodity at date when it did not exist redirects you
  to actual version
Merge pull request #94 from alphagov/55066242-content-not-found-enhancements

Enhance goods code not being found handling code