QmlDesigner.model: rename id is now a proper refactoring operation

I an id is now changed in the navaigator or property editor,
we now use the qmljseditor to properly refactor.

Also I changed dynamic_cast to qobject_cast

Reviewed-by: Erik Verbruggen

src/plugins/qmljseditor/qmljseditor.h

@@ -243,6 +243,8 @@ public:
     bool updateSelectedElements() const;
     void setUpdateSelectedElements(bool value);
 
+    void renameId(const QString &oldId, const QString &newId);
+
 public slots:
     void followSymbolUnderCursor();
     void findUsages();