Added Vertical Centering behaviour

Signed-off-by: Kulamagal Mahendrarajah <kulamagal@qi-interactive.com>
Merge branch 'master' of https://github.com/qi-interactive/behaviors

Signed-off-by: Kulamagal Mahendrarajah <kulamagal@qi-interactive.com>

Conflicts:
	dist/behaviors.css
	dist/behaviors.min.js