[WO-03-020] Fix insecure Default in Implementation of BCC Feature (Low)

Display warning to user when using BCC feature

src/js/controller/app/write.js

@@ -200,6 +200,17 @@ var WriteCtrl = function($scope, $window, $filter, $q, appConfig, auth, keychain
     // Editing headers
     //
 
+    /**
+     * Warn users when using BCC
+     */
+    $scope.toggleShowBCC = function() {
+        $scope.showBCC = true;
+        return dialog.info({
+            title: 'Warning',
+            message: 'Cannot send encrypted messages with BCC!'
+        });
+    };
+
     /**
      * Verify email address and fetch its public key
      */

src/tpl/write.html

@@ -13,7 +13,7 @@
         focus-input-on-click>
         <div class="mail-addresses__more">
           <button wo-touch="showCC = true;" ng-hide="showCC">Cc</button>
-          <button wo-touch="showBCC = true;" ng-hide="showBCC">Bcc</button>
+          <button wo-touch="toggleShowBCC()" ng-hide="showBCC">Bcc</button>
         </div>
         <label>To:</label>
         <tags-input class="tags-input" ng-model="to" type="email" tabindex="1" add-on-space="true" add-on-enter="true" enable-editing-last-tag="true"