[develop] Updates to devclean.sh script and plotting scripts and tasks

[natalie-perlin]

DESCRIPTION OF CHANGES:

• ./devclean.sh script that cleans SRW builds is updated, all the cleaning tasks are done for the directories under the main SRW tree

• Documentation updated for the devclean.sh script changes

• plotting scripts updated to have geographical data visible over the colored fields

• plotting task updated to allow graphics output for individual ensemble members

• use python3 to checkout external sub-modules in a checkout_externals script; python3 is a default for other scripts; some systems such as MacOS no longer come with python2

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update (UPDATED)

TESTS CONDUCTED:

Tested various combinations of cleaning up tasks on MacOS

• [ ] hera.intel
• [ ] orion.intel
• [ ] hercules.intel
• [ ] cheyenne.intel
• [ ] cheyenne.gnu
• [ ] derecho.intel
• [ ] gaea.intel
• [ ] gaeac5.intel
• [ ] jet.intel
• [ ] wcoss2.intel
• [ ] NOAA Cloud (indicate which platform)
• [ ] Jenkins
• [ ] fundamental test suite
• [ ] comprehensive tests (specify which if a subset was used)

DEPENDENCIES:

DOCUMENTATION:

ISSUE:

devclean.sh script update addresses the issue in #1073 (devclean.sh demonstrates very unsafe directory removal behavior)

CHECKLIST

• [x] My code follows the style guidelines in the Contributor's Guide
• [x] I have performed a self-review of my own code using the Code Reviewer's Guide
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes need updates to the documentation. I have made corresponding changes to the documentation
• [ ] My changes do not require updates to the documentation (explain).
• [x] My changes generate no new warnings
• [ ] New and existing tests pass with my changes
• [ ] Any dependent changes have been merged and published

LABELS (optional):

A Code Manager needs to add the following labels to this PR:

• [ ] Work In Progress
• [ ] bug
• [x] enhancement
• [x] documentation
• [ ] release
• [ ] high priority
• [ ] run_ci
• [ ] run_we2e_fundamental_tests
• [ ] run_we2e_comprehensive_tests
• [ ] Needs Cheyenne test
• [ ] Needs Jet test
• [ ] Needs Hera test
• [ ] Needs Orion test
• [ ] help wanted

CONTRIBUTORS (optional):