Bring back tensorpy

For awhile, tensorpy stopped working due to changes in tensorflow.
Thanks to the release of https://pypi.org/project/tensorflow/1.15.4/, the following tensorflow issues / security vulnerabilities have been patched:

• GHSA-cvpc-8phh-8f45
• GHSA-63xm-rx5p-xvqr

New tensorpy Python requirements:

tensorflow==1.15.4
six>=1.11.0
requests>=2.18.4
Pillow==5.4.1
BeautifulSoup4>=4.6.0

tensorpy now has strict OS and Python requirements:

• A Mac or Linux machine
• Python 3.5, 3.6, or 3.7