Kokkos Refactor in MueLu (and Xpetra)

MueLu relies heavily on Xpetra to provide a multigrid package that can work both with Epetra and Tpetra underlying linear algebra. Xpetra was created to provide a unique interface to both Epetra and Tpetra objects. That being said MueLu also aims at performing well on next generation platforms (manycore, GPUs, the next big thing). To do so we decided to use Kokkos for code portability and also because Tpetra is using Kokkos. However Epetra does not support Kokkos and this means that some code in MueLu will require Tpetra as the underlying linear algebra package.

What are the build/run requirements of refactored code

The goal of this section is to defined constraints that the refactored code needs to comply with but also what additional freedom is granted in to refactored code vs. "regular" code.

Build requirements

The goal is to have all of MueLu including the refactored build with both the Epetra stack and the Tpetra stack.