speed_grader_json: load quizzes faster

this should provide a significant speed
boost to speed_grader_json for quizzes
by squashing a few N+1s (the most significant
N+1 being for Quiz loading). also made a tweak
to submission permission checks that should
improve performance.

closes CNVS-27323

test plan:
- create a quiz with submissions
- verify you can open the quiz in
  speedgrader

Change-Id: If069c52440e5981c872f57723e30d0d0665ec8ad
Reviewed-on: https://gerrit.instructure.com/73490
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Tested-by: Jenkins
QA-Review: KC Naegle <knaegle@instructure.com>
Product-Review: Spencer Olson <solson@instructure.com>

app/models/assignment.rb

@@ -1437,7 +1437,7 @@ class Assignment < ActiveRecord::Base
         map{|s| s.as_json(:include_root => false, :only => [:user_id, :course_section_id]) }
     res[:context][:quiz] = self.quiz.as_json(:include_root => false, :only => [:anonymous_submissions])
 
-    includes = [:versions, :quiz_submission]
+    includes = [:versions, :quiz_submission, :user]
     includes << (grading_role == :grader ? :submission_comments : :all_submission_comments)
     submissions = self.submissions.where(:user_id => students).preload(*includes)
 
@@ -1524,6 +1524,12 @@ class Assignment < ActiveRecord::Base
                                    elsif quiz && sub.quiz_submission
                                      qs_versions[sub.quiz_submission.id].map do |v|
                                        qs = v.model
+                                       # copy already-loaded associations over to the
+                                       # model so we don't have to load them again
+                                       # when qs.late? gets called
+                                       qs.quiz = quiz
+                                       qs.submission = sub
+
                                        {submission: {
                                          grade: qs.score,
                                          show_grade_in_dropdown: true,