MFEM kernel updates

[artv3]

This WIP PR addresses issues: #578 along with major clean up passes...

Relevant kernels will be checked to be consistent with MFEM-4.9. FOM will be updated to be the DOF

Checklist:

• Convection
• Diffusion
• MassPA (remove from procurement list)
• MassEA
• MassVec
• MassAtomic
• Add MassVec direct tuning
• Add MassVec loop policy (without template increment)

[rhornung67]

@artv3 please check for compiler warnings and squash them in this PR. There are some related to unused variables (defined in macros) in develop. I would have fixed them, but I didn't want to get in your way.

[artv3]

I think this PR should now be good to go, @rhornung67 I fixed the compiler warnings as well.

[MrBurmark]

This is generally looking pretty good, but its hard to see what's really changed among all of the refactoring.