Proposal for minimal changes to EDV Data Model to support Hubs

1. JWE headers may contain synchronization primitives (vector clocks / hash links / counters, CRDT_TYPE)
2. A new HTTP endpoint `/sync` should be exposed, and it should leverage the JWE headers to return a result set of EDV Documents.
3. EDV Documents with JWE Headers including `CRDT_TYPE: AutoMerge` contain AutoMerge deltas.

### Developer user story

1. Developer creates a new Vault for Music
2. Developer creates a new AutoMerge Document Music Playlist with ID 123
3. Developer shares access to Vault with 3 Other Applications (Tablet , Phone, Home Server)
4. Applications construct and submit AutoMerge Deltas as Documents.
5. Developer calls `/sync` on tablet....
6. Hub Client on Table uses EDV client to pull down all deltas for ID 123, and applies auto merge and returns a JSON object containing changes from 3 devices with no conflicts.