ENYO-1636: Make ExpandableListItem header moon.Item
ENYO-1636: Make ExpandableListItem header moon.Item

Issue:
- ExpandableListItem header is currently set as a control.
- Disabled control is focusable.

Fix:
- Change header kind as moon.Item so it can get spotlight focus.

Signed-off-by: Kunmyon Choi <3510e15fb820b511597698c69f7aab7153d9a537@lge.com>

enyojs/moonstone