improve/tidy up interfaces widget

Attempt 2 with ipv6 fix. Assuming the address in the screenshot is long enough.

The fix, had to change class on line 91 from "vncellt" to "listr". Which is weird as original it was "vncellt". This means we lose the alternative colour scheme. But I think it looks better then the original widget.

Ready for review

![widget](https://cloud.githubusercontent.com/assets/4223752/3987312/51072660-28a4-11e4-9451-a4ee1bd47f3f.png)

Edit: Centered status icons, and made IP address bold (not shown in old screenshot above)
A couple of points here:

* Indent is broken, using spaces instead of TABs
* If ipv4 is set and ipv6 not, &lt;br&gt; won't be a problem, then the code can be simplified like:
```
if (ipv4 is set):
  print ipv4;
  print br;
endif;

if (ipv6 is set):
  print ipv6;
endif;
```