Add http timeout parameter (implement feature #88)

  Setup unicorn and nginx http timeout.

  On a little vm, sometime nginx fail to load the page. (with a error 502).
  Default value for unicorn is 60 and for nginx it's 300 (cf.<F12> https://github.com/gitlabhq/gitlabhq/issues/694)
Manage unicorn_workers (refs: #88 and #89)

  The default value is 2 workers