Migrate fields/functionality from Quiz to Assignment

[krishnans2006]

This improves general model relationships and paves the way for future quiz improvements (like #9).

It also renames LogMessage to QuizLogMessage to both clear existing log messages and make the name more readable.

[krishnans2006]

Here's a script that successfully migrates assignments to the new structure:

from tin.apps.assignment.models import Assignment, Quiz

for assignment in Assignment.objects.all():
    if Quiz.objects.filter(assignment=assignment).exists():
        q = Quiz.objects.filter(assignment=assignment)[0]
        assignment.is_quiz = True
        assignment.quiz_action = q.action
        assignment.save()
        print("*", end="")

[JasonGrace2282]

Overall, looks good to me!
Left some comments, but could you also add the ability to enable/disable autocomplete on quizzes?

[krishnans2006]

could you also add the ability to enable/disable autocomplete on quizzes?

I meant for this PR to just be a one-to-one migration, without adding new features; I'd like to make sure that everything is set up properly first. So, autocomplete will probably be in a follow-up commit/PR (along with #9 and other planned improvements).

[krishnans2006]

Update: the code snippet above had a typo. For documentation purposes, here's the code that was run on production:

from tin.apps.assignments.models import Assignment, Quiz

for assignment in Assignment.objects.all():
    if Quiz.objects.filter(assignment=assignment).exists():
        q = Quiz.objects.filter(assignment=assignment)[0]
        assignment.is_quiz = True
        assignment.quiz_action = q.action
        assignment.save()
        print("*", end="")

The output was

*****************************************************************************************************************************

meaning 125 assignments were changed. 🎉