New port: science/py-tensorflow-estimator: TensorFlow Estimator, an API to simplify machine learning programming

Dependencies are unusual for science/py-tensorflow-estimator:
science/py-tensorflow imports science/py-tensorflow-estimator in its python code,
but science/py-tensorflow-estimator is a separate project that depends on science/py-tensorflow
in order to build.

PR: 226400
Submitted by: Anthony <amzo1337@gmail.com>