Move drilldown to Treetable and create the year-to-year links inside WidgetLink.

I've also changed the example to use Slovakia's kosice dataset.
First version of TimeSeries widget.

The code uses Rickshaw and is based on Treemap's.
Add ability to change TimeSeries' renderer.

Now you can pick from any of Rickshaw's renderers, like line, bar or stack.
Timeseries uses Aggregate API endpoint.

The pagesize set from outside of the widget controls the number of entities on
the visualization. I didn't simply pass that to the Aggregator because it
defines the TOTAL number of elements (i.e. if there's only one entity with 200
entries, it'll be the only shown). I think controlling the number of entities
makes more sense.

The bad side is that I'm not limiting the actual Aggregator's pagesize. Even
though we'll only show 10 entities (for example), we'll get them all. This
causes a big performance hit on huge datasets. This definitely is something
worth looking into afterwards.
Timeseries creates all elements that it needs on the page.

The knowledge that it needs a div for the legend, yAxis, etc., should only be
inside itself. The only reason someone from outside should care about its
existance is for styling.
Add Query Builder support to Timeseries.