[#64] Showcase specification

Please use this Pull Request for discussion related to the new CKAN 'Showcase' feature (aka, Related Items). **DO NOT MERGE** until the spec has settled (likely when the feature is released).
I think generic names losing meaning and understanding. There are always going to be edge cases that make you want to use a more general name, but that is a trap. The excellent analysis shows that 25 out of 40 sites call it Apps, 6 sites call it "Apps & Ideas" (probably because it is a default - I don't think anyone apart from DGU actually lists Ideas), and no other name has caught on beyond a single site.