stop polling NotificationManager for now notifications, instead handle notifications on demand. This gets rid of the 50ms timer that was burning energy unnecessarily.

This change introduces a special meaning to IOManager::addTimer(-1, 0) in order to get a new virtual function without breaking BC.

Additionally a previously inlined function was moved to the .cpp file. The only place where this breaks (that I know of) is in kdemultimedia/arts/midi/audiotimer.cc. It only needs a recompile of kdemultimedia to fix it, though.