Fixes#440
We previously weren't observing changes so they weren't being
automatically propagated. We were using an old pointer which at best
returned the wrong value and at worst crashed. I was able to make it
crash eventually, too.
This changes the fields to be properly published and observed and as a
result the config is immediately available to all users.
Previously, this would crash. Once the crash was fixed, it would hang
because we would only show confirmation if the terminal window had
focus.
This introduces some medium complexity logic to work around this:
1. If we are the key window, then show the confirmation dialog. Done.
2. Otherwise, if any other window is a terminal window and is key,
they're going to take it so we do nothing.
3. Otherwise, if we are the first terminal window in the application
windows list, we show it even if we're not focused.
