QmlDesigner: Adding watcher

This watcher checks the directory for the QML file
and triggers an item library update if e.g. a component is added.

Change-Id: Ic130c73d70d328482543cd981f8fba9566d3ab4b
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/plugins/qmldesigner/designercore/metainfo/subcomponentmanager.cpp

@@ -481,6 +481,8 @@ void SubComponentManager::update(const QUrl &filePath, const QList<Import> &impo
         addImport(ii, imports.at(ii));
     }
 
+    m_watcher.addPath(newDir.absoluteFilePath());
+
     parseDirectories();
 }