Include puns colormaps

[SteSeg]

Hi! I noticed that the plotter does not allow for perceptually uniform sequential colormaps (e.g. viridis, cividis, plasma etc.). This PR includes them.
It was sufficient to substitute:

mcolormaps.datad

with:

mcolormaps._gen_cmap_registry()

in docks.py and plotgui.py files.

[paulromano]

I'm wary of relying on a function that is intended to be private (use of leading underscore). It looks like the same thing can be achieved with:

import matplotlib.pyplot as plt

plt.colormaps()

[SteSeg]

Right, I didn't realize that. I switched to those lines now. Thanks!

[paulromano]

Thanks @SteSeg!