Lattice that shows played MIDI notes

[Andreya-Autumn]

The lattice graphic can do two cool things for us. It can show which 12 notes are presently in our tuning. It could also take in a MIDI stream and show which notes are being played (like in the Gary Garett video linked in the Readme).

Currently we are doing the former only. I really want to also do the latter.

Few options for how to do this:

Could make this an optional feature of the main plugin.
...Or give it a pop-out window which does the note visualisation (while the main keeps showing the mapping)
Or alternatively, write a second plugin which does visuals-only.

I really like the last idea UX-wise. Especially because it could potentially let you put a few visualisers on different tracks. Know how tracker/chiptune folks make those four-quadrant videos with oscilloscopes? Imagine that but with lattices showing a bass part, melody, chords etc.

But of course, that would be require some state sharing between instances, which requires IPC. Which JUCE provides, but I'm not sure how easy it would be to implement. Investigate!