[BUG #8560] use 'justify' as default alignment
[BUG #8560] force visibility update for selected page
[BUG #8560] fixed base calls
[BUG #8560] fire an event if a child widget was added or removed
[BUG #8560] fixed tearDown
[BUG #8560] replaced disconnectChild method with removedChild event
[BUG #8560] selected property  now stores the button
[BUG #8560] listen for the widget's addedChild and removedChild events
[BUG #8560] fixed tabBar tests
[BUG #8560] replaced connectPage method with addedChild listener
[BUG #8560] check for parent
[BUG #8560] fixed tab page