Distinguish between intermediate and final feedback

* Also add more information to user_exercise_feedback
* Migrate existing feedback to enrich with submissions

db/migrate/20201019090123_add_normalized_score_and_submission_to_user_exercise_feedback.rb

@@ -0,0 +1,23 @@
+class AddNormalizedScoreAndSubmissionToUserExerciseFeedback < ActiveRecord::Migration[5.2]
+  def change
+    add_column :user_exercise_feedbacks, :normalized_score, :float
+    add_reference :user_exercise_feedbacks, :submission, foreign_key: true
+
+    # Disable automatic timestamp modification
+    ActiveRecord::Base.record_timestamps = false
+    UserExerciseFeedback.all.find_each do |uef|
+      latest_submission = Submission
+                          .where(user_id: uef.user_id, user_type: uef.user_type, exercise_id: uef.exercise_id)
+                          .where('created_at < ?', uef.updated_at)
+                          .order(created_at: :desc).first
+
+      # In the beginning, CodeOcean allowed feedback for exercises while viewing an RfC. As a RfC
+      # might be opened by any registered learner, feedback for exercises was created by learners
+      # without having any submission for this particular exercise.
+      next if latest_submission.nil?
+
+      uef.update(submission: latest_submission, normalized_score: latest_submission.normalized_score)
+    end
+    ActiveRecord::Base.record_timestamps = true
+  end
+end