Custom Window loading

[gm9]

/signed

Making window loading self-sufficient in the way it is done for default UI windows would be quite helpful as it would allow UI elements to completely reside within the Custom tree and still show automatically. A simple tag on the window's root page like ShowOnLoad would be enough, further scripting can be done via the OnShow event.

Additionally, I'm running into lag problems with my SubclassDetection on slow systems when triggered right upon UI load, so a LoadDelayed property to load a window only after everything else has been initialized would be sweet.