Spin-and-brush support

[dicook]

When you are trying to cluster data, it can be useful to use a spin and brush approach.

1. Start with all points same colour (don't know the clusters)
2. Tour until see a cluster (gaps), and brush this group of points a selected colour
3. Continue touring until another cluster emerges, brush this group of points a different colour
4. Repeat 3 until no more clusters can be seen

[pfh]

This feature is a bit more complex than I want to include in this widget, but I would like it to play well enough with other Javascript or Shiny code to allow someone to implement. It could make for an interesting project.

I think all the pieces are there with Javascript. The Javascript object has method renderValue, which could be used to add new groups with different colours, getState/setState to manipulate the current selection, and emits "changeSelection" events when the selection changes. Would need to use setState after a renderValue to keep the current projection and velocity.

(I am much fuzzier on what would be needed with Shiny.)