Add ability to update superusers via the UI

Fixes #634

static/js/pages/superuser.js

@@ -160,6 +160,31 @@
       }, errorHandler)
     };
 
+    $scope.setSuperuser = function(user, status) {
+      var setSuperuser = function() {
+        var params = {
+          'username': user.username
+        };
+
+        var data = {
+          'superuser': status
+        };
+
+        ApiService.changeInstallUser(data, params).then(function(resp) {
+          $scope.requiresRestart = true;
+        }, ApiService.errorDisplay('Could not change user'));
+      };
+
+      var msg = 'Note: This change, once applied, will require your installation ' +
+                'to be restarted to take effect';
+
+      bootbox.confirm(msg, function(status) {
+        if (status) {
+          setSuperuser();
+        }
+      });
+    };
+
     $scope.showDeleteUser = function(user) {
       if (user.username == UserService.currentUser().username) {
         bootbox.dialog({