Add checkbox and make sure to uncheck it after submission

lms/static/coffee/src/staff_grading/staff_grading.coffee

@@ -328,6 +328,7 @@ class @StaffGrading
     @error_container.html(@error_msg)
     @message_container.toggle(@message != "")
     @error_container.toggle(@error_msg != "")
+    @flag_submission_checkbox.prop('checked', false)
 
 
     # only show the grading elements when we are not in list view or the state

lms/templates/instructor/staff_grading.html

@@ -78,7 +78,9 @@
   <h3>Written Feedback</h3>
   <textarea name="feedback" placeholder="Feedback for student (optional)"
             class="feedback-area" cols="70" ></textarea>
-</div>
+<p>
+   Flag as inappropriate content <input class="flag-checkbox" type="checkbox" />
+</p>
   
 
 <div class="submission">