Adapt to Python 3.7 and TensorFlow 2.0

[StSchulze]

These changes allow DeepNovo to be run with Python3.7 and TensorFlow 2.0 (there will be deprecation warnings but in principle it works).

In addition, requirements.txt has been added to allow installation of all required Python packages.

import resource and the corresponding print statement has been removed from deepnovo_main_modules.py to avoid this requirement.