Scrubbing FastTree learners

[Ivanidzo4ka]

Sub task of #2613
FastTreeBinaryClassificationTrainer
FastTreeRankingTrainer
FastTreeRegressionTrainer
FastTreeTweedieTrainer
BinaryClassificationGamTrainer
RegressionGamTrainer
FastForestClassification
FastForestRegression

and their base classes.
Also note how everywhere in code we call AlgoTypeOfTask for our trainers and in GAM it's opposite.

and their base classes