Metrics

[BaruchG]

What does this PR do?

Continuation of #887 and replaces our iou and giou with torchvision versions.

Fixes part of #839

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[akihironitta]

How about removing these functions instead of having the exact same things with different names? Or are we keeping these for backwards-compatibility?

[otaj]

Yeah, @akihironitta, this is for backwards compatibility.