Add dark mode favicons and template to overwrite favicons

[dpgraham4401]

Description of changes

1. Creates a SVG ninja star favicon to accompany the PNG version
   • Also use this SVG file in the djang-ninja docs
2. Cleans up the pixelation of the PNG, which we can keep for compatibility with older browsers that do not support SVG favicons.
3. Places the favicons in a separate django template and document overriding it as a way for downstream projects to supply their own favicons for the swagger/redocs API documentation pages.
   • we can pull this part out since it may disrupt the current way that people are doing things.

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[dpgraham4401]

Forgot to mention, this closes #1541