publish subscribe mechanism for Widgets

```
Move the periodic widgets to a publish/subscribe mechanism versus the current
periodic polling. Polling every second for OSPF adjacencies for example can be
quite CPU intensive.

Would be nice to define in a modular way data that can be collected and then
displayed on the canvas. For example different EMANE models may have different
ways to report throughput.

A first (easy) step may be adding a configuration item for the number of
milliseconds for polling (e.g. large scenarios could refresh every 5 seconds
versus every 1 second.)
```

Original issue reported on code.google.com by `ahrenh...@gmail.com` on 18 Jul 2013 at 5:43