Further pack messages for QQmlProfilerService

Allow multiple detailTypes in each packet and extend the profiling code
to make use of that. Note that this changes the usual order of
pixmapSizeKnown and PixmapLoadingFinished events. As far as I can see
this doesn't affect the QML profiler frontend and the order of these
events isn't specified anywhere.

Change-Id: Id39ad98594ccf35add4415e08daf9e92ab561237
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>