Reimplement eventdispatcher

The current eventdispatcher does nothing but call native ProcessEvents, sendPostedEvents and Window system events in an endless loop. That causes all applications to use one core to its fullest.

On desktop windows we use ProcessEvents in conjunction with a custom event to be send, so that WaitForMultipleObjectsEx returns in case we want explicitly the dispatcher to run.

StopProcessEvents could be used from some other thread maybe? But definitly we need to get a better solution.