Split `settings.BASE_DIR` into `MODULE` and `DATADIR` #3723

Job	Run time
Linter	2m 23s
Test + Coverage	2m 55s
Test (shuffled order)	2m 31s
MyPy	1m 51s
Backup process	3m 13s
Compile Scss	1m 40s
Build nix environment on MacOS	3m 45s
Formatting	1m 36s
Render Html pages	1m 51s
Test Typescript	2m 1s
	23m 46s

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