Make use_cuda parametric for CPU use

[devrimcavusoglu]

I'm currently adding Prism to Jury. Current implementation forces using GPU if cuda.is_available() returns True; however, this behavior is problematic as a user is unable to use CPU e.g if VRAM is not sufficient for loading the underlying prism model. It'd be very good if use_cuda is exposed as an option to user, so the user can decide whether to use CPU/GPU.

Refer to note on obss/jury#79.

[thompsonb]

I don't think the default behavior should change but an override makes sense. I have limited time to work on this now, but I can try to review a PR.