introduce test file for Efl.Ui.Group_Item
this tests that the tree structure which is defined by the group and
child item hirachy is correctly transformed into a linear list.
This also checks that the bug from the revision before is not happening.
Depends on D9890
Reviewers: segfaultxavi, zmike, cedric
Reviewed By: zmike
Differential Revision: https://phab.enlightenment.org/D9872