Upgrade from version 2 to 3 of the Amazon Skills API

[dbudwin]

Anything you'd want to know about the API can be found here: https://developer.amazon.com/public/solutions/alexa/alexa-skills-kit/overviews/understanding-the-smart-home-skill-api

This seems like it should be pretty straightforward, it mainly just adds some new fields to the existing API. Most of the changes will occur in API/DevicesController.

For example, this will allow us to take advantage of the new field displayCategories to make sure devices in RoboHome are grouped correctly in the Alexa app.