Proper way to apply select2.

Also, fixes a hidden bug that doesn't expose itself right now, due to
the fact that Explorer is essentially a single route at present. Once we
have more than one "page", i.e. when we add a second endpoint, this bug
would have surfaced.
Use md5 to generate document IDs.
trade-event model
trade-events routes
trade-events controllers.
searchHeader property.
Tweaks to ITA design changes.
Complete trade-event model and results page.