Initial mesh implementation [newfield_revision]

[Scott Haney]

I just checked in

UniformRectilinearMesh<Dim, T>
NoMesh<Dim>

into the newfield_revision branch. These were reviewed by Stephen and 
represent the first part of mesh functionality: constructors and 
accessors. Note that I have removed coordinate system from the mesh 
concept because it fundamentally has nothing to do with meshes, which 
simply map index locations -> coordinate locations. I'll bring 
coordinate system back into the system in the functors that will be used 
to compute positions, volumes, etc.

Scott