Research multi-hop communication via social mesh

Identify one or more possible solutions for propagating end-to-end encrypted data over the "social mesh" of connections between Briar users, by allowing devices to relay data they don't subscribe to.

Identify and evaluate any risks of passive information leaks or active attacks. Evaluate performance (e.g. fraction of messages delivered, delivery latency, bandwidth and battery use) taking the current single-hop sync as a baseline. Recommend whether any of the solutions should be incorporated into Briar.