VotingClassifier should have a way to access fitted estimators by name

[jnothman]

VotingClassifier provides named_estimators which is a dict of constituent estimators before fitting (i.e. the estimators are cloned and individually fit when the VotingClassifier is fit). These are already accessible through get_params(). More useful would be a named_estimators_ or similar containing the fitted estimators from estimators_.

[amueller]

I vote for bunch to enable tab-completion (not sure if named_estimators is a bunch).