Stick Plot Option for Combo Plot

[Daniel Marsh-Patrick]

This works like the barcode plot, except it will run from the centre to the edge of the violin (whereas the barcode is a consistent width all the way down).

[Daniel Marsh-Patrick]

I've done some reviewing and refactoring of code to try and make this work. Unfortunately, getting the stick plot to render is a bit tricky at this time due to needing to know where the data point will intersect with the KDE plot. This is probably better being planned out and the barcode plot does what we want without the signficant overhead.

I'll keep some of the refactoring as it will help extend the combo plot later on if needed, but for now I'm going to put this on hold while I think about it some more.

Useful reading:

• http://bl.ocks.org/duopixel/3824661
• https://bl.ocks.org/bricof/f1f5b4d4bc02cad4dea454a3c5ff8ad7