Clean up configuration

Make it easy to configure (via code) whether to use wifi/ethernet/null,
and make it easier to configure how the pulse sensor should be
interpreted (to make it more interesting when testing with push-buttons)
Fix crash issues with Wifi

Now we're just left with unreliability issues.  Hopefully short-term
watchdogs will work around that?
Config tweaks

Need to figure something better out for this..
Merge pull request #116 from RightpointLabs/WiFiForNetduino

Rework config and get Wifi working