Return 404 for unknown Location/Clients.

It assumed you'd never ask for a unknown URN, and the page exploded with
a 500.
Fix invalid class names in Locations#show.

Puts a basic test of Microformats2 correctness on the documents.
Merge pull request #31 from G5/validate-microformattyness

Fix invalid class names in Locations#show.
Merge pull request #30 from G5/handle-unknown-urns

Return 404 for unknown Location/Clients.