Rip modal_xulG_stack out, replace with openDialog

Rip modal_xulG_stack out, replace with openDialog

This converts the util/window.js open function to a wrapper around the
openDialog function and passes xulG in that way, as well as teaches
global_util.js to look for it having been passed in via the arguments
parameter on window.

The non-modal "push it into place" is still done as well, in case some
window isn't using global_util.js and needs xulG.

Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>