Label abbreviations based on only plotted intervals

[willgearty]

As it is, the abbreviations in the built-in data are unique abbreviations based on the full set of intervals, etc. This means that for any individual plot, the abbreviations may be more unique (i.e., longer) than needed for the set of intervals that are in the plot. It should be fairly easy to, within an individual plot and individual timescale, automatically generate unique abbreviations based on only the list of the intervals that are being shown/used.