QmlJS: Add error message for invalid root item in the designer

Documents with those types do crash the qmlpuppet and confuse the users.
With this patch we give a clear error message and such files are not supported
anymore.

Change-Id: Iba19def2751d4dc81d90684c0c63c0274fdf49cf
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -221,6 +221,8 @@ StaticAnalysisMessages::StaticAnalysisMessages()
             tr("Qt Quick Designer only supports states in the root item."));
     newMsg(WarnAboutQtQuick1InsteadQtQuick2, Warning,
             tr("Using Qt Quick 1 code model instead of Qt Quick 2."));
+    newMsg(ErrUnsupportedRootTypeInVisualDesigner, Error,
+           tr("This type is not supported as a root element by Qt Quick Designer %1."), 1);
 }
 
 } // anonymous namespace