Button to use all available GPUs

[mrviviano]

So I was wondering if you could add a button to the cuda devices tab that will allow the render to use all GPUs that octane can find.

I am using a render farm with a few nodes, but they all have different combinations of cards. When I go from a computer with 1 card to a machine with 2, it only will use 1 of the cards for the render. This even happens when I leave all GPUs unchecked in the cuda devices tab.

Thanks!
Matt