test_genlist: Refactor genlist focus test.
test_genlist: Refactor genlist focus test.

- Add more sample items.
- Clear genlist on focus callback only for the specified item.
- Fix broken item index handling
- Remove unnecessary app data structure members.
- Free unused item class.

tasn/elementary,tasn/elementary,rvandegrift/elementary,rvandegrift/elementary,rvandegrift/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary