Going to work on @jamalex 's comment about settings.DATABASES being initialized from a default ASSESSMENT_ITEM_DATABASE_PATH

The easy solution seems to be that we should not let the ASSESSMENT_ITEM_DATABASE_PATH be configurable for now.

It's an odd case: We want CONTENT_ROOT to be configurable for serving media, yet we need a database connection established on the basis of where CONTENT_ROOT points. I would suggest to leave it out of the docs.

In a longer perspective, things like settings.DATABASES should always be configured through ENVIRONMENT, it's a suitable "high-level" approach for this specific setting and that would also follow from normal conventions.

We could mention settings.DATABASES in the docs instead, but it's kind of a heavy chapter and people who want to mess with it are better off reading the source code and the django documentation.

Another issue regarding this is about the system-wide assessment items.... they might mean that the database is in a different location, forcing this logic to be pushed back the settings.base :(

Okay, so do assessment items count as user data or application data? In one sense they are application data since they are associated with a version, but in another sense they are user data since they can be downloaded after installation and their location on disk is configurable. (Though this is not the case in Windows! where assessment items are bundled with the installer.)

What are the likely cases where the end-user will install ka-lite and download the assessment items separately?

@MCGallaspy
Yes, to summarize our current situation: We offer an assessment-free version (understandably since its 500 MB) where users download the items into their USER_DATA_ROOT. But we also offer bundles where they will be available from a system-wide location.

The most likely cases are:

1. For devs, we constantly change ka-lite and the assessment items, so we need an easy way around it
2. Testing: We shouldn't put 500 MB of system data on the test server
3. Users with online access: They will find it easier to install a light-weight KA Lite and then download the assessment items if they need them - some might just want videos?
4. THE FUTURE! Assessment items might be available from separate sources.

This PR is very critical, as there are no one else who have expressed a desire for a review, I'm going to merge it so we can see if it works.