Adding a configuration flag:  enable_pnp4nagios

I have added a new config flag: enable_pnp4nagios.  This behaves similarly to enable_graphite, and removes unwanted elements from the status views if pnp4nagios is not in use.

I have never used github before today, so please be gentle if I have broken any etiquette, here.

Thanks,
Pete Morgan aka smartattack on #adagios

You should also fix indentation, the project uses a 4 space rule should look like 
```
    if adagios.settings.enable_pnp4nagios:
        try:
            tmp = run_pnp("json", host=host_name)
            tmp = json.loads(tmp)
        except Exception, e:
            tmp = []
            c['pnp4nagios_error'] = e
        c['graph_urls'] = tmp
```