eo: declare Eo stable

eo: declare Eo stable

Summary:
This declares the main part of Eo.h as stable, except the domain api for
now. We don't have a user of that API for now, nor do we have bindings
supporting threads, lets wait with this bit until we have bindings for
this, so we can test it.

Further more, this does not stabilize the composition API of
efl_object.eo.h, reason for this is, that we might want to overthink the
solution we have with events, as we might want to forward events per
default.
Depends on D7931

Reviewers: stefan_schmidt, cedric, zmike, segfaultxavi

Reviewed By: cedric

Subscribers: #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7932