Support the new protobuf fields.

- Full support for UNTYPED type.

- Receptive support for timestamp_ms (i.e. the processor can process
  it, but the client library cannot yet create it - which is kind of
  intended as timestamps are meant for other things like federation,
  which will need separate support anyway).

Change-Id: I5913164a80089943d49ad58bf86e465a843ab82b