Element: Make onDOMEvent fix focusout in addition to focusin

Using the exactly same approach, but listening to blur instead of focus.

Parameterized the event handling code so all that was needed to support
focusout was to create a separate instance parameterized with
'focusout' instead of 'focusin' and 'blur' instead of 'focus'.

Change-Id: Iee53b526aa7c6c1a20fda33872132e3014e0d290