Create setup.py script for OONI
We need a setup.py script to allow the installation of the software and for integration with the build system.
We are currently using requirements.txt for keeping track of dependencies. There are some tricks that can be done to make sure that setup.py also reads from requirements.txt.
Inspiration on how to do this can be drawn from the setup.py script of APAF: https://github.com/globaleaks/APAF/blob/master/setup.py