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What is the purpose of this PR?

Addresses a few incorrect and missing features in the mass plotting notebook.

• Adds dpi and fig_size to both cohort_cluster_plot and color_segmentation_by_stat
• Fixes incorrect sorting of colors when the colormap file is provided in cohort_cluster_plot
• Adds interpolation "none" to color_segmentation_by_stat to prevent interpolation of the cell borders
• Incorrect colors are properly reported back to the user
• Adds an option to save the plot as any other format accepted by matplotlib

How did you implement your changes

Added those small changes. The reason the colors were not mapping to the cluster appropriately was because the NumPy Array conversion to the colormaps didn't take into account that the colors need to be sorted w.r.t their associated cluster id.

Remaining issues

N/A.