feat(medcat-demo-web-app): CU-869b855n0 Simplify model access

[mart-r]

This PR simplifies model access.

It also makes some minor changes to the Dockerfile. That's because the previous setup was somewhat odd (in terms of makemigration, for instance).

It adds a little helper bit to the api callback for people unable to get the API key:

This shows a little helpful message, links to the UMLS license and the quiz about it:

The quiz looks something like this:

When everything is correct, you get an API key and a link:

When some answers are incorrect, you're put in a cooldown:

When trying to resubmit during cooldown:

When trying to restart quiz during cooldown:

PS:
I have already created (generated and validated) a set of questions I can add.

[tomolopolis]

Task linked: CU-869b855n0 Simplify access to free / open models

[mart-r]

Will go with #230 most likely