Implement scatter plot in measurement table & two measure classifier

[alanocallaghan]

First draft implementation of two measurement classifier and scatter plots in measurement viewer (along with histograms). Ideally I think these two panes should be merged, with an X and Y dropdown. If X or Y alone is selected, or if ==Y, then do a histogram. If both are selected and different, do a scatter plot. Saves space and I doubt many people will want to see histogram & scatter plot at the same time.

Two measurement classifier currently uses composite classifier, but really it should be something like a "union" classifier... or some kind of logical operand classifier. But I'm not currently sure what or how. The point colours on the scatter plot should also probably live update.

The code here is horrendous and needs to be refactored in both cases, but works as a POC.

[alanocallaghan]

Also tbc whether the scatter plots here are replaced with a more lightweight version that doesn't create a billion JavaFX nodes, or whether we just subsample the points for display