Upgrade so Oyente can run with Python2 & Python3

[vietlq]

Currently Oyente supports only Python 2.7 which is being phased out soon. Time to upgrade. Most of changes are simply adding parentheses to print x => print(x).

The process is rather simple: https://docs.python.org/2/library/2to3.html

If you are OK @luongnt95 I can help to do this & create a PR.

[vietlq]

@luongnt95 Also web3.py requires Python >= 3.5 and < Python 4, so basically the tool itself requires 2 different versions of Python to run: 2.7 for Oyente and 3.5, 3.6 for web3.py. That's really unclean and I suggest to migrate to Python3 and fully use Python 3.5 for additional benefit for type annotation for safety: https://www.python.org/dev/peps/pep-0484/

Happy to help with migration bit by bit.

[luongnt95]

Oyente currently uses six package to support both python2 and python3. And Yeah, the installation has the problem with web3 when the py2.7 version of web3 is deprecated now. Just feel free to make a PR

[suhabe]

@luongnt95 Is it possible to build oyente from source at the moment, given the web3/py2.7 issue?

[luongnt95]

@suhabe I think this #301 can help at the moment

[lazzarello]

#336 should address this using the Ubuntu update-alternatives system. Check the Dockerfile for references or just run the code in an image built from that Dockerfile.