Symbian: need to set the window group name from a Qt API

The application name S60 displays in the task switch window is taken from the window group name.
So that the application developer can localise this name, or change it dynamically, it needs to be settable using an existing Qt API.

It seems to me that using the title of the main window would be consistent with other platforms.
The developer suggested QCoreApplication::setApplicationName() originally, but this isn't consistent with other platforms.

Implementation is simple, i.e. S60->windowGroup().setName(blah), once we decide the correct API