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

common/lib/capa/capa/templates/schematicinput.html

 <span>
-  <input type="hidden" class="schematic" height="${height}" width="${width}" parts="${parts}" analyses="${analyses}" name="input_${id}" id="input_${id}" value="" initial_value=""/>
+  <input type="hidden" class="schematic" height="${height}" width="${width}" parts="${parts}" analyses="${analyses}" name="input_${id}" id="input_${id}" aria-describedby="answer_${id}" value="" initial_value=""/>
 
   <div id="value_${id}" style="display:none">${value}</div>
   <div id="initial_value_${id}" style="display:none">${initial_value}</div>
@@ -13,13 +13,21 @@
 
   <span id="answer_${id}"></span>
   % if status == 'unsubmitted':
-  <span class="ui-icon ui-icon-bullet" style="display:inline-block;" id="status_${id}"></span>
+  <span class="ui-icon ui-icon-bullet" style="display:inline-block;" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: unsubmitted</span>
+  </span>
   % elif status == 'correct':
-  <span class="ui-icon ui-icon-check" style="display:inline-block;" id="status_${id}"></span>
+  <span class="ui-icon ui-icon-check" style="display:inline-block;" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: correct</span>
+  </span>
   % elif status == 'incorrect':
-  <span class="ui-icon ui-icon-close" style="display:inline-block;" id="status_${id}"></span>
+  <span class="ui-icon ui-icon-close" style="display:inline-block;" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: incorrect</span>
+  </span>
   % elif status == 'incomplete':
-  <span class="ui-icon ui-icon-close" style="display:inline-block;" id="status_${id}"></span>
+  <span class="ui-icon ui-icon-close" style="display:inline-block;" id="status_${id}" aria-describedby="input_${id}">
+    <span class="sr">Status: incomplete</span>
+  </span>
   % endif
 </span>