Improvement - Disable reload of nginx when enabled=False (previously the nginx was always reloaded if settings.config != None; even with enabled=False)

Removed comment after testing that this change works with xenial

Fixes #70

Build NGINX from source with nginx.ng state with support for passing
compile time flags necessary for installing modules such as more headers
by the openresty project.

On Ubuntu, you can take advantage of Personal Package Archives on Launchpad simply by specifying the user and archive name.  On other apt-based systems this must be the complete entry as it would be seen in the sources.list file.

This is crap but configuration for http scope cannot be both ordered and
merged from map.jinja it seems, see issue #40.

To resolve the occurrence of the below error, a dependency has been added to require the nginx user first be created, either by nginx package installation or explicitly with salt (when installing nginx from source).

```
----------
          ID: /var/www
    Function: file.directory
      Result: False
     Comment: User nginx is not available Group nginx is not available
     Started: 15:50:02.070799
    Duration: 0.531 ms
     Changes:
----------
```

* added comment for pillar example
 * removed override releasever variable use for CentOS