Re-enable cvnDB and ensure error handling

It seems jQuery 1.8.3 (currently used by MediaWiki) doesn't
take care of handling errors for cross-domain JSON (e.g. when
the server doesn't respond or when the hostname can't be
resolved). It seems that the latest jQuery does handle these
errors, but for now adding fallback to timeout which should take
care of handling these. Better than nothing at all.

Fixes #28