Add scale options to window menu

This is a workaround against bug #504368, which makes QEMU window text blurry if resized. This is a common and annoying problem:

http://butnottoohard.blogspot.com/2010/01/qemukvm-windows-7-blurry-text.html
http://unix.stackexchange.com/questions/60564/how-can-i-restore-default-window-size-in-kvm-qemu


The ability to resize window is a feature - it allows to adjust viewport of QEMU to the convenient working area. But there should be an option to restore the size of the window or scale it like 1:2, 2:1 etc. I don't know about if that should be exposed to QEMU monitor as some "window <command>" set , but it would be extremely convenient to provide at least Ctrl+Alt+U functionality through window level menu.

Ubuntu 13.04, QEMU 1.4.0