List: Focus set on item content objects, the item content objects should be checked...

List: Focus set on item content objects, the item content objects should be checked whether type widget or not.

Summary:
Upon focus set, if the item content object is not of type widget
(could be of type Evas_Rectnagle) focus set/get is not possible.
ERR<17428>:eo lib/eo/eo.c:603 _eo_call_resolve() in elm_widget.eo.c:112: you called func 'elm_obj_widget_can_focus_get' (239) which is unknown in class 'Evas_Rectangle'.
ERR<17428>:eo lib/eo/eo.c:788 _eo_api_op_id_get() in elm_widget.eo.c:212: unable to resolve regular api func 'elm_obj_widget_child_can_focus_get' 0xb75e6f40 in class 'Evas_Rectangle'

Test Plan: elementary_test -to "list focus" (make focus_on_selection enabled and give a right key event when a content object is focused)

Reviewers: seoz, SanghyeonLee, eagleeye

CC: seoz
Differential Revision: https://phab.enlightenment.org/D972