Implement a simple "hello world" web server in Python and hook it into
SlapOS infrastructure, so that newcomers can see how to implement
SlapOS services:

    - start service from under etc/service/
    - add promise for service monitoring
    - publish connection url

TODO IPv4 frontend
------------------

For now the service is only accessible via IPv6, because SlapOS provides
an unique ipv6-address to every computer partition, and provided IPv4
addresses have non-global scope and can be used only for organizing
internal subservices.

The way we handle IPv4 publish - is through explicit additional IPv4
frontend - TODO add example how to do it.

TODO monitoring
---------------

Currently in SlapOS for a service in order to be monitorable, the
service needs to explicitly extend from monitoring stack:

    http://git.erp5.org/gitweb/slapos.git/blob/HEAD:/stack/monitor/README.txt

TODO - add example how to do it.

Cc: Jérome Perrin <jerome@nexedi.com>