Waveform & Spectrogram Multicursor

[KinMaynard]

When called as individual plots both waveform & spectrogram have multicursors, however, when plotted as subplots inside the visualizer function only the multicursor referenced last works. I suspect this is due to matplotlib widgets requiring a reference to them so as to avoid garbage collection. I suspect once the second multicursor is referenced the former is garbage collected.

Directions to proceed:

1. Research & implement how to keep references to 2 multicursors
2. Have no multicursors in visualizer
3. Another annotation method (Click point to display coordinate values)
4. Use mouse event to enable reference to multicursor when mouse over relevant plot (waveform or spectrogram)

Relevant Matplotlib Docs 1
Relevant Matplotlib Docs 2