Make Atlas more robust to inconsistent Onionoo replies
When Onionoo lists a relay in its summary document but doesn't have a details document for that relay, Atlas will run into a "TypeError: relay is undefined" in js/models/relay.js in $.getJSON() in the lookup function. The effect is that Atlas shows "undefined" in its results. The fix is for Atlas to not rely on Onionoo always having a details document. (The other fix is to make Onionoo not return inconsistent replies, but that's something that the database-based Pyonionoo will fix.)