Add bicubic interpolation for PyTorch SiamFC

[arbitularov]

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[ClementPinard]

Thanks for you PR !
However, I suspect this is going to be very slow
I was going to link the PR that added bicubic interpolation to pytorch, but I saw you like comments there ! :p

Anyway, the official implementation is guaranteed to be faster and is already available on pytorch nightly builds.

A good thing to do might be to try to import it from pytorch, and then define the function if the import fail.

[arbitularov]

Oh, ok, I see. Thanks for your advise. I will try it ))