package/python-web2py: new package

This patch adds web2py package. web2py is a free open source
full-stack framework for rapid development of fast, scalable, secure
and portable database-driven web-based applications.

[Thomas: fixup symbolic link to the systemd service file.]

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>