Make KLibLoader a K_GLOBAL_STATIC which get's cleaned up a little later now.

This at least fixes Phonon cleanup where the backend would be deleted before Phonon's internal Factory object was deleted.

If this change introduces new crashes on shutdown make sure that the code in question doesn't rely on KLibLoader destruction. It should rather define how and when cleanup happens.

Moved private function into the private object and removed the d pointer which is replaced by the K_GLOBAL_STATIC in the .cpp file.

There's still a private slot left, but Q_PRIVATE_SLOT cannot be used without d pointer...