Add SpaceEvenly to flex justification

Add SpaceEvenly to flex justification

Flex justification uses Yoga Layout's justify-content.
Up to now, SpaceEvenly of Yoga Layout's justify-content has not been
added to flex justification.

SpaceAround distributes the equal space to before, and after each item.
Therefore, the space between adjacent items is twice bigger than the
space between the beginning edge and the first item.

To distribute the equal space to before, between, and after each item,
SpaceEvenly is added to flex justification.

Change-Id: Icb4e1f1aa74f52a5cfe8f1399e9f42457c8c081f