Disentangle the covariant returns and introduce
convenience accessors.
Move internal classes away from Qt4Project.

Change-Id: I6c3158988824d2a159b1b3f8ecdf8432c32be2bc
Reviewed-on: http://codereview.qt.nokia.com/3216


Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>