Add a 'ready' event to the window open sequence
Add a 'ready' event to the window open sequence

This is so any required initialisation can happen after 'open'
which guarantees the window is visible, but before 'ready' where
the subclass can override it.

Change-Id: I6f3dd974627a36aaba423c10ae4f3be59b913111

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui