Branch to v2.x and increase the SDK version

This will automatically prevent 1.x apps running on 2.x firmware,
and vice-versa.  This has a matching change in tintin.

NOTE: I don't intend to pull this, but I want someone to confirm that we do want to have a separate branch for v2.x.  Having a separate branch requires more integrations, but allows bugfixes to the 1.x we currently ship between now and 2.x release.