Currently, as a python3 interpreter, specific version has been chosen.
As fs-uae-wrapper doesn't use any special features from latest version
of the python3, it doesn't make sense to have fixed version of it. Just
let operating system pick right python 3 interpreter.
Also, new command was added to utils - run_command which is an
generalized subprocess.call function.
Requirements is now added with module six, which was needed to detect
string-like objects in sane way.
