Do not rely on anything in LightChild, make answer completion persistence self-contained

mentoring/public/js/answer.js

@@ -4,6 +4,12 @@ function AnswerBlock(runtime, element) {
         init: function(options) {
             // register the child validator
             $(':input', element).on('keyup', options.blockValidator);
+
+            var checkmark = $('.answer-checkmark', element);
+            var completed = $('.xblock-answer', element).data('completed');
+            if (completed === 'True') {
+                checkmark.addClass('checkmark-correct icon-ok fa-check');
+            }
         },
 
         submit: function() {

mentoring/templates/html/answer_editable.html

-<textarea
+<div class="xblock-answer" data-completed="{{ self.completed }}">
+  <textarea
      class="answer editable" cols="50" rows="10" name="input"
      data-min_characters="{{ self.min_characters }}"
      >{{ self.student_input }}</textarea>
-<span class="answer-checkmark icon-2x"></span>
+  <span class="answer-checkmark icon-2x"></span>
+</div>

mentoring/templates/html/answer_read_only.html

-<blockquote class="answer read_only">
+<div class="xblock-answer" data-completed="{{ self.completed }}">
+  <blockquote class="answer read_only">
     {{ self.student_input|linebreaksbr }}
-</blockquote>
-
+  </blockquote>
+</div>