ENH add sample_weight support to dummy classifier
Merge pull request #3418 from arjoly/dummy-weight

[MRG] ENH add sample_weight support to dummy classifier
DOC update what's new
DOC sample_weight attribute
FIX: Remove raw_coef_ attribute that eats up memory
Modified sparse OvR to handle sparse target data

Defaulted label binarizer to set sparse_output=True when training ovr
classifiers, edited Label binarizer to allow for sparse binary column output
DOC fix docstrings; add @hamsal to authors
split test_common.py into checks and test file.
move dataset generation into estimator_checks
some cleanups in common_test, speedup.
Make fit_transform and fit().transform() equivalent in nmf
slight speedup
some cleanup