Investigate django-split-settings as an alternative to our current nested imports

[mrmachine]

https://github.com/sobolevn/django-split-settings

Currently we have a settings module in ICEkit which attempts to import/override various settings modules local to ICEkit and/or the project. This might make things a bit easier to understand.

[mrmachine]

I've done some work on this in ixc/ixc-django-docker#1