Added a wrapper to hold individual devices updates.
With surrounding serialization list wrapper, no longer need to
duplicate device ids in every update message.  Can just use device id
from singleDeviceUpdateList.
Use a SingleDeviceVersionResponse to generate a serialized protocol buffer message that other side can use to reconstitute SingleDeviceVersionResponse on its end.
Added a protobuf message type for version query responses.
Instead of returning all updates, allow to query for only updates that match fields, or are within particular ranges.
Added a fixme message to code warning about longs' signedness.
Renamed class.  Intention is to store full histories of updates in SingleDeviceUpdateList rather than to just use it for a one-off message.