Removed reference to authToken from Account

This was a race condition that could prevent
multiple devices from authenticating simultaneously.
AuthTokens are ephemeral and single-use so don't
need to be managed by the Account.
when uid is null, don't get account from kv
move keyfetchtoken to cache
account may be null on /account/keys
Merge pull request #174 from dannycoates/i174

Can KeyFetchTokens be ephemeral?