Rename accounts to users to be consistent with the new naming scheme
where account only referes to the logged in user of the session and
implement live updates of users via a user store which listens for
updates from the event stream.
Rename and refactor the types passed over the API to be based on an
entity that's either living or a tombstone. A living entity has a
deleted property that's either undefined or false, while a tombstone
has a deleted property set to true. All entities have a numeric id
and an updatedAt timestamp.
To sync entities, an array of replacements are passed around. Living
entities are replaced with tombstones when they're deleted. And
tombstones are replaced with living entities when restored.