Simple way of selection the used GPU?

[iyukar]

Being able to set the GPU in the menu would be convenient if the default isn't the ideal one.
In my case it selects the right one, and I'd only occasionally want to use the slower one when generating video in the background, but in some cases the wrong GPU in a multi-GPU system might end up being the default.
Having a selection option would help a lot in this case and it would be more convenient if you like to switch often.

In case someone is looking for a way to change the used GPU, it's possible to change the device by editing cli_args.py
changing the line
parser.add_argument("--cuda-device", type=int, default=None,
To a device number.