Allow creation of invalid remus::proto::Job objects.
Correct MeshIOType to properly serialize empty strings.
Update the Job UnitTest to verify it can serialize an invalid job.
Update remus::proto::Message to use MeshIOTypes serialization code.

Previously Message was manually de-serialzing the MeshIOType which is
bad, since MeshIOType has a serialize and de-serialize routines and those
should be used instead.
Merge pull request #140 from robertmaynard/make_invalid_jobs

Make invalid jobs