Separate data into one ephemeral (deltas) and another persisted log (snapshots)

[adzialocha]

Automerge gives us both some sort of Operation-Message and Full-State-Messages, that is, interfaces to retrieve both the encoded representations for Operation-based CRDTs or State-based CRDTs (haven't checked the exact internals of Automerge, but I guess that's how it works). Other Text-CRDTs implementations will give us a similar functionality.

To account for the two different natures of these data types we want two separate p2panda append-only logs maintained per document:

1. "State" log which has a max. depth of 1 (it prunes itself directly on every new appended operation) holding the full State-based-CRDT "snapshot"
2. "Delta" log which is not persisted (ephemeral) and used to gossip live changes like keystrokes etc. to other peers