Custom colormap(s) for plot.flow()

[jondo]

... would be nice to have, but are not implemented yet, see

neurite/neurite/py/plot.py

Line 297 in 249d497

raise Exception("custom cmaps not currently implemented for plt.flow()")

(Sorry, I can't take the time to offer a patch.)

[adalca]

@jondo agreed, but also limited by time :). I'll keep this open in case someone finds the time to help us out!