requirements

@floop I'm still thinking about the cxflow installation process.

I still think we should keep .requirements in order to preserve the standard package structure and for possible further deployment to pypi repository. Hence, it should be fully installable via pip.

However, I see advantages in system package manager. I restructured the pacakges accordingly to the way they might be installed (pacman > pacaur > pip). I wonder if we could create a simple script that would walk throug the reqs file and try to install each line (prefixed with python) by pacman (on failure pacaur (on failure pip)). It will be OS-specific of course, but ubuntu has old versions of system packages anyway so why bother.

What do you think?