We were painting unfinished pixels while waiting for the WebContent
process to render the page. This caused OOPWV to flicker black
sometimes, which looked pretty bad.
This way we still flicker, but at least we flicker with the correct
palette color. :^)
This isn't entirely symmetrical with on_load_start as it will also fire
on reloads and back/forward navigations. However, it's good enough for
some basic use cases, and we can do more sophisticated notifications
later on when we need them.
Every widget now has a GUI::FocusPolicy that determines how it can
receive focus:
- NoFocus: The widget is not focusable (default)
- TabFocus: The widget can be focused using the tab key.
- ClickFocus: The widget can be focused by clicking on it.
- StrongFocus: Both of the above.
For widgets that have a focus proxy, getting/setting the focus policy
will affect the proxy instead.
