Fixing handling of adding custom OIDs in UI (#653)

* is_critical wasn't in the schema, so was getting dropped.
* isCritical in the Javascript wasn't getting assigned if it was unchecked. Now, it will be assumed false if missing.
* The display of critical or not in the list of added custom OIDs was unclear when it was just true/false with no heading. Now it will be displayed as critical or nothing instead.
* The namespace for the checkbox for isCritical was wrong, and didn't get processed with the oid/type/value variables.

lemur/static/app/angular/authorities/authority/extensions.tpl.html

@@ -196,7 +196,7 @@
     <div class="col-sm-2">
       <div class="checkbox">
         <label>
-          <input type="checkbox" ng-model="authority.extensions.custom.isCritical">Critical
+          <input type="checkbox" ng-model="authority.customIsCritical">Critical
         </label>
       </div>
     </div>
@@ -208,7 +208,7 @@
           <td>{{ custom.oid }}</td>
           <td>{{ custom.encoding }}</td>
           <td>{{ custom.value }}</td>
-          <td>{{ custom.isCritical}}</td>
+          <td>{{ custom.isCritical ? "critical" : "" }}</td>
           <td>
             <button type="button" ng-click="authority.removeCustom($index)" class="btn btn-danger btn-sm pull-right">Remove</button>
           </td>