Fix inability for >1 graph controller to show data

[#46027763]

Model event listeners extend the d3 (internal!) event dispatch system. This system only allows 1 listener per (eventName, event namespace) pair. See https://github.com/mbostock/d3/wiki/Internals#wiki-dispatch_on 

Therefore, in order to allow multiple graph controllers to listen to model events, it is necessary for each graph controller to use a different event namespace.