Server block LWRP and nxensite/nxdissite script

Created a LWRP for creating, deleting, enabling and disabling nginx server blocks. And added site enable / disable script written by @perusio
[Here's the reason](https://github.com/phlipper/chef-nginx/pull/17/files#diff-56db1e575dc13d306523511891509c1bR38)