Improve error handling during initial connection w/ WebUSB

Originally an idea from @tannewt.

We may want to force users to re-connect their boards to WipperSnapper during the initial registration process to allow IO to debug errors "for them".

Error messages during this process would be piped over serial as JSON-formatted packets. IO would be able to process/understand the state of the board's JSON error/success packets and relay human-readable "next steps" to a user.

This could also be handled by the last step of the "New Device" workflow where there would be a "Still not connected?" option which would open this "debug mode".

It may be presented to the user as a "step" in the "New Device" workflow to make the process sit on one end of the site.

cc @lorennorman for technical feedback/comments

Start by tracing the initial registration process and the last step of the New Device workflow. Review how serial communication currently handles board state, then define the JSON error and success packets and the user-facing next steps needed for a debug mode. Done means the reconnection flow and its error handling are specified across the board and IO workflow.

Written by the indexing model from the issue text.