Use prob more strictly inside SSD and Faster R-CNN

[yuyu2172]

We should use prob whenever possible.

[Hakuyume]

We cannot assume that all models return a value in [0, 1] as a confidential score.
We should define the API to fit all models.
It is confusing that SSD and Faster R-CNN return probs and another model returns scores.

[yuyu2172]

None of them return probs. The internal naming is changed to be more explicit.

[Hakuyume]

None of them return probs.

Sorry, it's my misunderstanding.

The internal naming is changed to be more explicit.

Using both score and prob is confusing. I don't think this modification improves readability.

[yuyu2172]

Using both score and prob is confusing. I don't think this modification improves readability.

I agree. It is not necessary to enforce this rule.

[Hakuyume]

LGTM