Combine draw-tsp-path.py and draw-tsp-path-concorde.py into one file

[matthras]

It finally clicked for me why I was so annoyed about having two separate scripts despite both of them using the same 'canvas' for drawing to PNG files so I was effectively having code duplication.

In general I'm thinking the general flow process should be: "Check if there's a Concorde solution, if not, solve for a solution using OR-tools. Draw image" because in general the Concorde solution returns a better solution but for licensing purposes some people might want to keep things strictly in Python, so it's nice to have the versatility there.

I'm going to work on this for #2 to begin with, then once I've figured that out I'll apply it to this one as well.