Begin sending notifications based on all accounts.

We need to notify frontends of notifications for every account
(wallet), not just the "current" opened account, since wallet will
need to have multiple wallets open at the same time.  Frontends will
have to filter notifications to show only details of only one account
if they need to display just one account at a time.

As of this commit, account balances and lock state notifications are
using this per-account notification scheme.