scoping event handlers to the chart

[gordonwoodhull]

chart.registry.js is okay, but as its name suggests, it was supposed to be a substitute/generization for the dc.js chart registry.

We're using it for all kinds of events which really should be scoped to the individual chart.

In particular, it looks like you can't have two charts with move_nodes active on the page. Probably the second chart erases the event handlers for the first one.