event: add STICKY_MULTY events

event: add STICKY_MULTY events

Add a new event flag for sticky events so that multiple events of that type can
be stored on a pad at the same time. Change the _get_sticky_event() function to
loop over the multiple events of a type.
Change the foreach function to make it possible to removed and modify the sticky
events on a pad.
Use an variable size array now to store the events. This could later be
optimized some more.