provide a callback after interface is loaded

[x37v]

Currently I am doing styling by executing a function in the 'oninit' callback for the last element in my interface.. I figure this is something useful to a lot of people and it would be cleaner if there was a way to access the interface and provide a callback for 'after init' of the entire interface.

[charlieroberts]

That seems easy enough to add. Maybe just call a window.oninit() method that can be overridden in interface files?