QmlProfiler: Set objectNames to QmlProfilerCanvas instances

Helps debugging ...

Change-Id: I9d6508e05e5f581f7d43f4b015fcfd4596f5d5ec
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
QmlProfiler: Make sure UI is properly rendered

Do the QML based painting when requested inside the UI thread, and
only copy the final canvas pixmap in the renderer thread (in paint()).
To avoid excessive re-drawing delay the painting via a timer to the
next event loop run.

The previous logic was still from Qt Quick 1 times, where the paint()
method was called in the GUI thread. This has changed in Qt Quick 2:
Here the paint() method will be called (on Unix) in a separate renderer
thread, making the drawRegion / onDrawRegion connections implicitly
deferred.

Change-Id: I298547013658e4cd1e94115305577bdb96cd0b2a
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>