Deprecate `clientId`

[alecgibson]

sharedb/lib/agent.js

Lines 22 to 28 in 346eb0c

	this.clientId = hat();
	// src is a client-configurable "id" which the client will set in its handshake,
	// and attach to its ops. This should take precedence over clientId if set.
	// Only legacy clients, or new clients connecting for the first time will use the
	// Agent-provided clientId. Ideally we'll deprecate clientId in favour of src
	// in the next breaking change.
	this.src = null;