Plot options should be specific to each plot

[rambaut]

The 'Setup...' button on the toolbar for plots (such as the density plot) allows the user to set the range for an axis. Currently these options are universal for that plot irrespective of which trace is being examined. It would be better if it was specific to the trace being examined (so each trace has its own settings for each plot). However, I am not sure how this would work when multiple traces are selected. Perhaps a Map is used with keys being a Set containing the selected traces?