Use new colormap registry in matplotlib

[lkluft]

Also clean-up imports to be less cluttered in the import block and more verbose in-line.

[lkluft]

One might think about if it is the proper behaviour for functions like colors2cmap to register the colormaps, or if they should simply return an object. I guess for the "Typhon colormaps" it is fine to be registered under the ty: prefix, but the others seem to clutter the new registry.

[olemke]

How about adding a keyword to those functions to let the caller decide if the colormap should be added to the registry and set it to False by default to avoid unwanted cluttering of the registry?

[lkluft]

Sounds like a solution 👍 I will play around with both but will -- if at all -- deal with them in a separate PR anyhow