refactor to load recommender models generically from Classifier.load()
Model weights BINARY and None

Documents in a Model(weight=BINARY) will have document.vector with 0 or 1 feature weights. Documents in a Model(weight=None) will have document.vector with original feature weights (instead of the relative TF or TFIDF).
Merge remote-tracking branch 'jgrivolla/model_loading' into origin
update contributors