implement sticky_pattern option in unlearner
raise exception in anomaly/recommender when unlearner is full
clear unlearner when clearning model in nn-based recommender (ref #13)
support clear_row API for nn-based recommender
Merge remote-tracking branch 'upstream/develop' into sticky_unlearner

Conflicts:
	jubatus/core/classifier/classifier_base.cpp
fix for exception safety
Merge pull request #4 from kmaehashi/sticky_unlearner

implement sticky_pattern option in unlearner