New standards - Githubissues

PR checklist

[x] Describe the changes you've made.
[x] Describe any tests you have conducted to confirm that your changes behave as expected.

This PR updates the default styles, colors, palettes, and gradients to reflect the newest version of the style guide. This includes:

Changes to font sizes, line weights, etc. for matplotlib rcParams defaults
Addition of new colors for use in gradients and palettes and removal of deprecated colors
Refactoring gradients and adding new gradients
Refactoring palettes to deprecate old-style palettes, which were legacy groupings of colors from the original brand identity statement (Accent, LightAccent, etc.) in favor of new-style palettes, which are categorized based on their usage purpose (Primary, Secondary, Neutral, Background, etc.)
Small bug fixes here and there

Ignore the test script test_plotting.py; it will be replaced by the tests in #28.