Add index and filter combo box to external help window

Change-Id: Icc815379220c55d9d7dc5d154278ba21ce2e9984
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/help/localhelpmanager.cpp

@@ -253,6 +253,11 @@ void LocalHelpManager::setFilterIndex(int index)
     emit m_instance->filterIndexChanged(m_currentFilterIndex);
 }
 
+int LocalHelpManager::filterIndex()
+{
+    return m_currentFilterIndex;
+}
+
 void LocalHelpManager::updateFilterModel()
 {
     const QHelpEngine &engine = helpEngine();