Eina: Add Eina_Promise/Eina_Future.
This commit adds a new promise/future API which aims to replace
Efl_Object: Add integration with Eina_Future.
This commit adds the EO support for the new future infra.
From now on there's no need to efl_future_link()/efl_future_unlink()
object and futures since the new API already handles that internally.
Eina_Promise/Eina_Future: Add example and tests.