Wrap up floating point type and explore use of Boost::Multiprecision for arbitrary precision

[pbauman]

Definitely in the "would be nice" category.

Right now, I'm using libMesh::Real just about everywhere. I'm thinking we typedef a GRINS::Real which can default to libMesh::Real. Then, we can have room to explore trying to plug into Boost::Multiprecision if we ever want to do residual/Jacobian/other calculations in higher precision arithmetic.