Review fixes:

* nextprops -> nextProps
* give value a default of ""
* give groups a unique id

Test plan:
* Add multiple unit widgets, see that you can toggle the radio buttons
  in all of them!
* After a few seconds with a nonsensical answer in a unit input box it
  says "I don't understand that", but the message goes away when you
  start to type again.

Auditors: alex