[MEDIUM] updated log format to report frontend and backend

[MEDIUM] updated log format to report frontend and backend

The log format has been slightly updated to separately report the name
of the frontend and the name of the backend. The accept date has been
enhanced to report the millisecond. The number of remaining connections
has also been updated and their order reversed, to include the number
of connections on the frontend. The new log format is now :

  -  $1: IP:port
  -  $2: accept date in this format : [dd/mm/YYYY:HH:MM:SS.ttt]
  -  $3: frontend name
  -  $4: backend name '/' server name
  -  $5: req time '/' queue time '/' conn time '/' header time '/' total time
  -  $6: HTTP status code
  -  $7: number of bytes returned
  -  $8: captures (request)
  -  $9: captures (response)
  - $10: completion flags
  - $11: remaining conns on process '/' frontend '/' backend '/' server
  - $12: srv queue size '/' backend queue size
  - $13..: '"' full request '"'