Change the default action to produce a graph.

The default action creates data for a line graph which shows
the number of stories over a time line matching any query criteria
passed.
eg.
/?start_date=2014/01/01&end_date=2014/05/02&label=smart-answer&query=passport,visa,marriage,death,birth
gives statistics on stories labelled smart-answer broken down by
the phrases listed in the query param.