Put calls to QQmlVmeProfiler behind "if (enabled)" macros

The construction of arguments to those calls may be expensive and should
be avoided if we're not really profiling.

Task-number: QTBUG-35315
Change-Id: I558fa4cae6cf532d22193283f1ee2a3b680e2eee
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
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>