osx: create macosx_events to deal with keyDown events

On OSX with Cocoa enabled keyDown events are now handled with
addLocalMonitorForEventsMatchingMask:handler:. This allows to respond to
events even when there is no VO initialized but the GUI is focused.
osx: cocoa_common: use default wakeup period

Now that Cocoa's input handling is done on a separate thread from the playloop
it is ridicolously simple to have longer asynchronous sleeps when paused.