Localize Close button in standard modals (fixes #481)

gui/modal.html

@@ -10,7 +10,7 @@
       <div class="modal-body" ng-transclude>
       </div>
       <div ng-if="close" class="modal-footer">
-        <button type="button" class="btn btn-default" data-dismiss="modal"><span class="glyphicon glyphicon-remove"></span>&emsp;Close</button>
+        <button type="button" class="btn btn-default" data-dismiss="modal"><span class="glyphicon glyphicon-remove"></span>&emsp;<span translate>Close</span></button>
       </div>
     </div>
   </div>