Comment settings for question content types should default to "disable"

Issue Summary

When you install quiz module + question types today the comment settings for all question content types (/admin/content/node-type/[question_type]) defaults to "Read / write". This, I imagine, forces the vast majority of quiz users to disable comments for each type manually, so I believe the default settings for comments on questions should be "Disabled", and the people needing comments could enable it, rather than the other way around.

(we can also think of potential very confusing situations for users where you get a long answer question with one textbox for the answer, then a new textbox for a comment right beneath it..)