Eo events: Change event callback signature.

Eo events: Change event callback signature.

Change the Eo event callback signature to what suggested by Marcel
Hollerbach in the ML (Thread: EFL interface change - Animator).

This changes the signature of callbacks from
Eina_Bool cb(void *data, Eo *obj const Eo_Event_Description *desc, void *event_info)
to
Eina_Bool cb(void *data, const Eo_Event *event)

Where Eo_Event is a structure that holds these parameters.

This makes it less annoying to not use parameters (you end up using
EINA_UNUSED less), and allows for future extensions to callback
parameters.

@feature