MDL-41757 quiz statistics : limit subq and variant stat rows

and print min, median and max.

question/classes/statistics/questions/calculated.php

@@ -55,6 +55,12 @@ class calculated {
      */
     public $subquestion = false;
 
+    /**
+     * @var string if this stat has been picked as a min, median or maximum facility value then this string says which stat this
+     *                  is.
+     */
+    public $minmedianmaxnotice = '';
+
     /**
      * @var int total attempts at this question.
      */