A status UI spike.
Do not queue event search jobs on PUT.

A user may perform a GET on any event search at any time; however, it is
possible that we will not be able to service the request out of cache,
due to data expiration.  We therefore need an endpoint to explicitly
trigger a refresh.  However, once we've got that, there's not really any
reason left to queue items from two endpoints.

Well, "avoiding round-trips" could be a reason.  I'll have to see how
badly that one extra request per search hurts things.
Add Font Awesome for UI icons.

The _icons.css in this commit is an abridged version of the CSS that
ships with Font Awesome.  I might just throw the whole thing in once I'm
confident that it won't affect any other styles.
Use Font Awesome icons in the query status widget.
Richer query status reporting.

In particular, we now have:

1. A specification for the status JSON structure.  Unfortunately, it's
   buried in the model specs, but it's a start.
2. Explicit started and done notifications for all queries in a set.
   (Near-future task: these objects concern query sets, not individual
   queries.  Names ought to be fixed.)