Make data requests time based

Instead of asking for the last 100 rows, initial request asks for all
data within the past 24 hours.  Subsequent requests only ask for data
after the initial request or the last time data was requested and
returned.
Refactored dataSource into separate method.
Now using plain JSON feed instead of view

No longer using the “view” datasource, so I had to change how I
processed the response and constructed Incident objects.