Summary:
If the size or hints of a child changes, relative_layout need to update layout.
And, if a child is deleted, it should be unregisterd from relative_layout.
Depends on D8625
Test Plan: elementary_test -to 'efl.ui.relative_layout'
Reviewers: Jaehyun_Cho
Reviewed By: Jaehyun_Cho
Subscribers: cedric, #reviewers, #committers
Tags: #efl
Differential Revision: https://phab.enlightenment.org/D8626