elementary: fix potential race condition by using Eina_Future attached to the object.

elementary: fix potential race condition by using Eina_Future attached to the object.

I get some random segfault in elementary test suite pointing to this code. Most likely
we do not properly destroy the timer during destruction. Could be because we initiate
a delay while destruction is going on or something like that. Anyway, it is easier and
more robust to get it fixed by linking the lifetime of the timeout to the lifetime of
the widget as future allow us to do easily.

Reviewed-by: Marcel Hollerbach <mail@marcel-hollerbach.de>
Differential Revision: https://phab.enlightenment.org/D9298