Clean up trailing whitespace, make indent uniform across Message.h.
Dummy untested implemenation of Sensorino.cpp.
RelayService: typos fixed.
Partly redesign the Message class, add deserialization.

 * slash the header size by two.
 * always store current state as a raw buffer, ready to be parsed or
   sent over to the remote end.  This way when the user is ready they
   can just grab the raw buffer and send it through, and we avoid
   parsing stuff that we don't need.
 * also actually implement parsing of incoming raw buffers.
 * add all kinds of accessors for other classes to use.

Untested, and it looks like the integer coding is not correct (always
uses two bytes instead of depending on the value), but at least
serialization and deserialization should be symmetric.
Move private constants from Message.h to .cpp.
Fix usage of msg types in Service.cpp.
Implement Sensorino::onRadioMessage().
Implement Message::send().
Don't die on unparseable messages, parse as GARBAGE.