Switch to new format for settings.CACHES

This should prevent warnings from being displayed whenever the code is
imported.
(cherry picked from commit 5829d326fca496914c73c093f765482d3578acd6)
Merge pull request #617 from learning-unlimited/stop_shell_warning

Stop settings.CACHES warnings from bring printed at startup
Merge pull request #625 from learning-unlimited/stable-mar13

Merge stable release 3 into main