QmlProfiler: Make sure details for bindings are shown in Events pane

React to a second changed() signal from the simple model that is
emitted after the binding text has been retrieved from the local files.
This will rebuild the whole model effectively twice ... ideally we'd
just update the text, but it shouldn't be a performance problem, either.

Change-Id: I71a47f0faddd3938711e2e190f1e9c961be343e4
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>