QmlProfiler: Update timeline contentWidth also if width changes

As the contentWidth depends on both the width of the flickable and the
currently selected time range it should be updated if either of them
change. Otherwise we can miss changes and show stale data.

Change-Id: Iab9e17eef3490531175a2374fb3da0e0071f3bd1
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>