feat: support custom colors for data/MC plots

[alexander-held]

Adding a new colors argument to visualize.data_mc and visualize.data_mc_from_histograms (as well as visualize.plot_model.data_mc) that allows specifying color names per sample: colors={"signal": "red", "background": "blue"}. Colors need to be provided for all samples, otherwise an exception is raised. If colors are invalid, an exception will later on be raised via matplotlib. The default behavior is unchanged, falling back to the seaborn-colorblind colors.

visualize.data_mc_from_histograms was still missing the channels kwarg, this is now also included.

* support custom histogram colors for visualize.data_mc via new colors keyword argument
* support custom histogram colors in visualize.plot_model.data_mc
* extend color and channel filtering functionality to visualize.data_mc_from_histograms

resolves #381 (rest of that issue migrated to #265)

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d761e30) 100.00% compared to head (44c2666) 100.00%.

Additional details and impacted files

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