Add ATOM change feeds for Commodity/Chapter/Heading
Extract common change presentation code to single Change controller
Add proper anchor links to Measures

Links only for Commodity changes.
Focus on Measure row if accessed using anchored link
Specs to ensure changes feeds are rendered

Updated VCR as it was not recording requests for some reason
Add ATOM feed icon for Chapters/Headings/Commodities
Add Goods code change presenters
Deduplicate change fetching with a concern
Merge pull request #85 from alphagov/change-atom-feed

Change atom feed