update compose file to normalize networks and ports + doc URL
update compose file to normalize networks and ports + doc URL

 * Documentation URL / source for nginx reverse proxy

 * normalize networks: we want a global system-wide
   network (softwarefactorynet), and container specific networks for safer
   inter-container communications (e.g. sonarnet to talk between sonar and
   sonardb)

 * normalize ports: best practice is to always define ports as strings to avoid
   issues with YAML converting port values < 80.

laurent-malvert/software-factory