ENYO-3632: send a message to user in case of internal FSM error
ENYO-3632: raise error popup in case of fsm error
ENYO-3632: exec any pending call-back in case of fsm error
ENYO-3632: play pending event in state ready (whatever the event that led to ready)
ENYO-3632: don't call cleanup when designer is closed after an error
ENYO-3632: exec call-back in case of error coming from designer...

... This errors can happen only after an event that stores a call-back. So
not having a call-back to play is a bug.
ENYO-3632: Improved error handling in case of missing call-back