Future: LineGrabPlot enhancements

[bradyzp]

Some usability improvements that might be nice to add to the plot in future:

• Add an inset plot to the LineGrabPlotter that shows the users location when zoomed in significantly. For reference: http://gtk3-matplotlib-cookbook.readthedocs.io/en/latest/zooming.html Like the left side plot, but actually inset into the main Axes.
• Enable users to set/control the graphical decimation ranges (i.e. set the % where a specific slicer is applied, and specify step parameter for the slicer).
• Allow users to enable/disable decimation with a checkbox or radio button on the chart area.
• Display the current decimation level somewhere on the chart area.
• Investigate using a simple filter function as opposed to the simple slice/step to sample the array for graphical display.
• Allow user to manually specify data limits (specifically x-axis) for data sets that don't auto-scale well.

These are all low priority, and I just want to record some ideas for future use as I worked through the recent plot code improvements.