[Reviewer - Ellie] Add monit polling, and make /ping available on IPv6

Tested monit polling as follows:

```
$ sudo pkill -9 nginx && wget -O - --no-check-certificate --header="Host: localhost" http://[::1]/ping ; sleep 20 && wget -O - --no-check-certificate --header="Host: localhost" http://[::1]/ping
--2014-09-05 11:41:28--  http://[::1]/ping
Connecting to [::1]:80... failed: Connection refused.
--2014-09-05 11:41:48--  http://[::1]/ping
Connecting to [::1]:80... connected.
HTTP request sent, awaiting response... 200 OK
```

Tested IPv6 function by requesting:
* http://[::1]/ping with the Host header set to localhost (returned 200 OK from nginx)
* https://[::1]/ping (passed on to memento)
* http://[::1]/ping with the Host header set to memento.homedomain (redirected to https://memento.homedomain/ping)
* http://127.0.0.1/ping with the Host header set to localhost (returned 200 OK from nginx)
* https://127.0.0.1/ping (passed on to memento)
* http://127.0.0.1/ping with the Host header set to memento.homedomain (redirected to https://memento.homedomain/ping)