QmlDesigner.metaSystem: fix fot Qt Components

In the case of "." imports we loose the package name.
This patches "maps back" to QtQuick by default or maps to <cpp>
if the package name is empty.

Change-Id: Ibe8d782541d109049f3480c7dfd15de69d75da38
Reviewed-by: Christian Kamm <christian.d.kamm@nokia.com>