Add estimator/params to config

Add kwargs to `entry_point` instantiation process. This gives me extra flexibility that I will need to write an sklearn wrapper for pylearn2, where some parameters will not be set in `fit_and_score_estimator`, while minimally changing the existing interface (e.g. I could add `estimator/pylearn2` to config, but that seems messier than writing a pylearn2 `entry_point`).