Output a visual representation of the graph after all spacers have been tested

[susannasiebert]

This may aid in manually identifying which peptides could be removed or which peptides should be clipped or have more flanking amino acids added.

https://networkx.org/documentation/stable/reference/drawing.html has some notes about packages that would allow us to draw the directed graph created in pVACvector.

[susannasiebert]

I have looked into it and the resulting graph usually looks much too complicated to be useful especially once you go past 5 peptides to include in the vector. We should discuss if we still think that this would be useful.