Use MDL-37459 to add admin defaults for assignment module.

Exploratory testing of the new admin settings is required to see their affect on the settings screen of the assignment For each setting in /admin/settings.php?section=modsettingassign Change the default, advanced, locked and enabled flags (if available) After each change view the create new assignment page and verify that the change in the admin setting has changed the assignment creation form in an expected way. The expectations are that: Locking a setting will make it readonly Changing a default will affect the default value of that setting for new assignments (dates will be relative to midnight) Making a setting advanced will hide it behind a "Show more" link in the form