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.
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.)
A status UI spike.
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.