Make it obvious that data is updating

It's important that we don't leave stale data on display. I've seen this
a couple of times if an AJAX request doesn't return, for example.

No fancy transitions just yet, but clearing the results is safer than
nothing.

https://www.pivotaltracker.com/story/show/74506334

[Delivers #74506334]
Merge pull request #18 from sealevelresearch/update-indication

Make it obvious that data is updating