On OS X the application icon can be changed at runtime, so this adds a way
to set this via the QPlatformIntegration.
[ChangeLog][OS X] QApplication::setWindowIcon now changes the icon for the
application in the dock.
Task-number: QTBUG-43999
Change-Id: Ice298c0bd52f10f4866f37c6d3f20cf5419b7a1b
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@theqtcompany.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
