Migrate to v2 of the REST API

[petcupaula]

API Doc: https://io.adafruit.com/api/docs/

Note: the new version requires a username for retrieving data, which would require existing users of the app to enter this info.

[petcupaula]

Because this will impact the users, might want to release an intermediary version announcing the upcoming change. Or support both versions of the API for a while.