Node Explorer: poll for updates from status

[tylersmalley]

We should not rely on the user clicking the refresh button and should poll at a set interval (5 second default).

[tylersmalley]

Easiest solution would be to pull every 5 seconds (should eventually be configurable), and compare to the existing nodes. if it differes, then call "refresh" on the NodeExplorerProvider. Because of #182, calling refresh is very heavy and we should limit the use.