Support offline first Store via threads-store wrapping threads-client

[carsonfarmer]

This would provide a first step towards snapshotting and remote state sync.

From slack:

Essentially, something like CouchDB. We already have threads-store, which is an offline implementation of our Store (with Codecs etc). Right now, it is only used in threads-database to do all the reducer logic and then database grabs the output and stages it for sync with the network layer...

But instead of syncing it with the network layer, we could just use a "passthrough" Codec, than stages the actual updated objects (or even just a reference to them honestly), and then when online, these get pushed to threads-client as if they were done at that time.

So what you'd get is a local db that feels just like threads-database, but in the background, is using threads-client to push the data to a remote peer.

Obvi snapshots would be really good (and this is essentially just "mocking" that), but useful first step where the work is on the "client" side.

[carsonfarmer]

Superseded by #414