ecore: animator use eo_add() instead of eo_add_custom()

ecore: animator use eo_add() instead of eo_add_custom()

Summary:
- use defauld constructor instead of custom one.
- we don't allow construction of an animator with a NULL callback function,
  this is checked in overriden eo_finalize.
- we don't support changing this callback once the object is created,
  such calls will call ERR() and return.

see 46a78e8c and f92e5d50 for eo_add_custom() -> eo_add() details

Reviewers: tasn

Reviewed By: tasn

CC: cedric
Differential Revision: https://phab.enlightenment.org/D1113