Non superuser became able to run decanter

I think that it is good for non superuser can run decanter.

- Make to assign dynamically the value of user and group
    in 'config/devel.py'.

- A matter of permission, I have change path.
  if you run '/path/to/decanter.py -p 8080'.

  - pidfile
    /var/run/decanter_8080.py -> /path/to/gen/run/decanter_8080.py

  - logfile
  /var/log/decanter_8080-2013-05-11.log ->
    /path/to/gen/log/decanter_8080-2013-05-11.log