Summary:
focus_user and focus_object are similar classes. by merging them into
one mixin, we can maintain consistency.
Test Plan: make check
Reviewers: bu5hm4n
Subscribers: cedric, Jaehyun_Cho, woohyun, jpeg
Differential Revision: https://phab.enlightenment.org/D5734
This fixes some of the warnings generated by calling functions on NULL
objects. One of the main remaining points is to avoid unwanted warnings
on non-existing parts.
Ref T6326
Yeongjong Lee
Jean-Philippe Andre
Amitesh Singh
Marcel Hollerbach