Fix up the ora2 scores affected by the ORA2 bug: (edx/edx-ora2#628)

  For affected assessments:
    - Sets PeerWorkflowItem.scored = 0 if currently = 1
    - Recalculates the score for the submission
    - If new score > old score, update the Score.points_earned with the new score
    - Updates TrackChanges.edited_content by prepending course staff message
Merge pull request #146 from Stanford-Online/dcadams/fix_ora2_scores

Fix up the ora2 scores affected by the ORA2 (edx/edx-ora2#628) bug.