AnswerGSHook: Produce AnswerFV TSV output in confidence order

This somehow already happens but may be just an implicit artifact. Order
of correct answers will matter soon.
AnswerScoreLogistic: Update the model
AnswerGSHook: Generate a record only for the top-ranked correct answer, not all of them

The hope here is that we will learn a sharper preference for features
that are usual though not necessary for finding the answer. However, it
will make our set more imbalanced.
AnswerScoreLogistic: Update the model