Python3.4+ and modern versions of TensorFlow/Keras support

[Vladkryvoruchko]

This PR will bring versions support to Python3.4+ and modern versions of TensorFlow/Keras

Ideally, PSPNet will run on every Python, starting from 3.4+

Issues(the same idea):
#63
#49

As discussed in that issues .h5 and .json models generated by Keras(python3.5), are not supported in python3.6
This is a very general issue, that can occur again on some other versions, even if solution for this case will be provided.

• Put .npy weights on my personal DropBox: .npy weigths #45
• Download .npy weights on the first run and convert them with current version of Python and Keras.
• Load only .npy weights and converting to .h5 .json automatically must resolve Can't load .h5 weights #56
• Update to a newer version of TensorFlow/Keras/Scipy and resolve all incompatibilities with different Python versions starting from Python3.4+. Define best combinations if needed
• Define better environment in requirements.txt/README.md: Environment not well defined #38