adds in aria attributes and semantic status content for option input problems

common/lib/capa/capa/templates/optioninput.html

 <form class="option-input">
-   <select name="input_${id}" id="input_${id}" >
+   <select name="input_${id}" id="input_${id}" aria-describedby="answer_${id}">
       <option value="option_${id}_dummy_default">  </option>
       % for option_id, option_description in options:
           <option value="${option_id}"
@@ -13,12 +13,20 @@
   <span id="answer_${id}"></span>
 
   % if status == 'unsubmitted':
-  <span class="unanswered" style="display:inline-block;" id="status_${id}"></span>
+  <span class="unanswered" style="display:inline-block;" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: unsubmitted</span>
+  </span>
   % elif status == 'correct':
-  <span class="correct" id="status_${id}"></span>
+  <span class="correct" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: correct</span>
+  </span>
   % elif status == 'incorrect':
-  <span class="incorrect" id="status_${id}"></span>
+  <span class="incorrect" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: incorrect</span>
+  </span>
   % elif status == 'incomplete':
-  <span class="incorrect" id="status_${id}"></span>
+  <span class="incorrect" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: incomplete</span>
+  </span>
   % endif
 </form>