22 get cmap is deprecated in matplotlib

[JesseSandberg]

Description

This fixes a Warning from matplotlib and replaces a code block in the notebook with a one-line function call. Plotting.py is now a file that will continue to grow as we add PRs.

Usage Changes

No user-impacting changes (other than the user no longer gets a Warning and the user sees slightly less unecessary code)

Todos

Notable points that this PR has either accomplished or will accomplish.

• Replaces deprecated matplotlib command with modern one
• repackages all colormap lines into one function called make_custom_colormap()

Pre-Review checklist (PR maker)

• Does the figure look the same no matter which cmap you use?
• New functions are documented
• Make a testing nb

Review checklist (Reviewer)

• put the cmap_test notebook in the python directory of DTA, add a lipid and a path, and run the cells.
  cmap_test.zip
• Do the two heatmap figures look identical?
• New functions are documented
• New functions/variables are named appropriately
• I understand what the changes are doing and how
• I understand the motivation for this PR (the PR itself is appropriately documented)

Status

• Ready for review

Not finished review