put nginx logs in the same place where other nginx logs are to be found
rename sites-enabled to just sites
add documentation for the nginx role
add two new roles

supervisor

* add supervisor package
* config it
* enable and start supervisor daemon
* the role has a parameter -- services -- a list of supervisor services
  to be created: see roles/supervisor/templates/service.conf.j2 for
  parameter list (probably should go to a overall doc of sort)

supervisor-service

* to be documented
add virtualenv role
start working on actual configuration of nine.bb.net