Support MeshTypes in JobRequirements

[robertmaynard]

As described in #5 we need to add mesh types to Remus.

It is pointless to add mesh types to Remus unless we can use them inside a job's requirements. This requires an extension of the remus::common::ContentFormat types and more constructors for the JobContent class.

Lets say that we add a ContentFormat type of REMUS_MESH, we would need a way to give a remus::mesh::Mesh to a JobRequirements, so we would need to add the following constructor:

JobRequirements(remus::mesh::Mesh mesh,
                              remus::common::MeshIOType mtype,
                              const std::string& wname);

Here are the questions that we need to answer. How does MeshIOType interact with a users Mesh class? Does JobRequirements even care? Like JobContent how do we easily convert from a JobRequirements back to remus::mesh::Mesh?