Remove windows from focustracker when they're minimized

[Joel Thornton]

Remove windows from focustracker when they're minimized - this may alleviate need for .getTopFocusableWindow() completely and thereby simplify code that currently has to use an async callback to get the top focusable window. This should also help with Sidewise sometimes unminimizing a window immediately after the user had minimized it.

Also look into smart focus code and make sure that it doesn't try to smart focus a tab within a minimized window.