Depend on and be compatible with the opscode nginx cookbook

With some slight modifications, this cookbook can be made compatible to the opscode nginx cookbook (by be depending on it and including the default recipe of nginx instead of installing a package "nginx"). This is useful if gitlab runs together with other services that also require nginx on the same box. Two new attributes "listen_ip" and "listen_port" have been added to be able to control on which ip and/or port nginx should be serving requests for gitlab.