Find better way to track numerical signals

[thinkh]

Problem
An input range slide is bound to a signal, such as the selected year in the Gapminder example. When dragging the slider a series of signal events are fired. In case of provenance tracking that would result in dozens of nodes. What we need to track is only the final position of the slider.

Current solution
Directly grabbing the mouseup and touchend listener from the HTML input element.

Feature request
A more general solution would be better to not rely on the input element listener.