DynDNS status widget async update

The Dynamic DNS status widget performs remote operations to the www to check the cached dynamic DNS IP against the actual current public-facing IP. When an external link is slow, or particularly when the cable is plugged in (it seems up) but actually the internet is down, it takes a long time for a response from http://checkip.dyndns.com/ to time out. The dashboard page hangs in a half-drawn state (up to drawing the DynDNS status table) for up to 30 seconds.
This change puts the code that does these external operations into some ajax/Java script that runs after the dashboard has drawn up. Code concept unashamedly stolen from the system information widget.
DynDNS status widget add 5 minute refresh

It was easy to add the code to refresh the status every 5 minutes. I think 5 minutes is a reasonable refresh time for dynamic DNS.
Merge pull request #488 from phil-davis/master

DynDNS status widget async update