We were using verify_token="" to mean that the user was verified. We need a unique constraint on verify_token to prevent two users from getting the same verify link in their email. This means that if we have two verified users, they will both have verify_token="", which triggers the unique constraint. Oops. However, null is an exception to unique constraints, so we're now using that instead to mean verified.
* Regress from `lastSynced` to just `sequence` to start with something simpler
* Simplified payload: separate metadata, assume canonical way to hmac it together
* No more "wallet state" except as a simple wrapper on the front end
* Version number in wallet payloads
A few things at once because it was faster to get a demo out the door. Skipping most test implementation though I made failing stubs so I know what to fill in later.
* Get/Post WalletState
* downloadKey/email so that a second client can log in, and/or recover from lost client
* Test client in Python to demonstrate the above
* Organize into packages
