BUG: Fix for cython version checking closes #9827
closes #9827

Added a cython version check at the top of setup.py; minimum version of 0.19.1. If the minimum isn't met, _CYTHON_INSTALLED sets to false, so the installation can proceed if cython is not needed, but will fail if cython is needed (with an appropriate error message).

Two new travis jobs added to test install_conda and install_pydata flows for the old cython revision, and ensure that pandas setup fails with appropriate error messages. See https://travis-ci.org/ajamian/pandas/builds/58315862 for regression.
