Add state to OFT::Mergers::Case
Wire crawl up to CaseList

* This gets us a stub minimal-detail file for each merger case on crawl
* We're still visiting a load of pages for which we have no parse/save
Add CaseStore#find

* Should be able to get back to a case given a URL from a site
Add Kramdown

* (and Nokogiri, which had, er, disappeared)
Cases stuff some markdown into invitation_to_comment

* Not where it'll end up, probably, but the tag removal will be the same