Port Zanata Python client to Python 3

The end of Python 2 support in Fedora is quickly approaching - https://fedoraproject.org/wiki/Changes/Mass_Python_2_Package_Removal - many Python 2 only packages have bell already dropped and soon there will not even be a Python 2 interpreter available.

There, the Zanata Python client (https://github.com/zanata/zanata-python-client), which used by many projects in Fedora, including the Anaconda installer, to push and pull translations, should be ported to Python 3, so that it continues to be available in the distribution.