QtXmlStream classes live in QtCore, not QtXml. Also add a few headers
that are not implicitly included in Qt 5 any more. This greatly eases
transition to Qt 5 which not having any side effects on the Qt 4 build.

Change-Id: I1293ef4360015b885dcea8c4099e8e5b9e254c91
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>