SparseCoder

Would be nice to wrap/implement [`SparseCoder`]( http://scikit-learn.org/stable/modules/generated/sklearn.decomposition.SparseCoder.html ) for use with Dask-ML and Dask Arrays. This is useful for computing the sparse code that is associated with a precomputed dictionary.

Start by reading the linked scikit-learn SparseCoder documentation and reviewing how Dask-ML and Dask Arrays expose scalable estimators. Define the integration needed for sparse coding with a precomputed dictionary; done means SparseCoder is available for Dask-ML and Dask Arrays with coverage for that use case.

Written by the indexing model from the issue text.