Persist visualizations param settings

[michaelbromley]

When changing settings, the changes should be locally persisted so that when reloading the visualization, the defaults are not automatically loaded.

This also implies there should be some kind of "reset" method, to put all the params back to the default.

The design of this feature should be planned in conjunction with the "presets" feature, since they share many of the same requirements.

[michaelbromley]

Idea: we can assign a unique ID to any visualization by creating a hash of the name + strigified params object. This ensures that presets will be compatible with the exposed params. If the params change, the ID will change too, so any presets assigned to that ID will no longer be valid for the visualization.