Parallelization

[dylan-copeland]

Parallelization of ROM and FOM linear system assembly and solution, using HypreParMatrix.

This is the first step in parallelizing the library, focused on ComponentTopologyHandler and the Stokes and Poisson examples. Some things still remain to be parallelized and optimized:

• SubMeshTopologyHandler is not supported in parallel.
• MFEMROMHandler::Solve still has global vectors for reduced_rhs and reduced_sol.
• Some sparse matrices have their entries copied inefficiently, see PoissonSolver::CreateHypreParMatrix() and StokesSolver::CreateHypreParMatrix().
• InterfaceForm::AssembleInterfaceMatrices should use a sparse array of SparseMatrix pointers, rather than a dense Array2D.
• MFEMROMHandler::CreateHypreParMatrix should use a sparse array of blocks.
• For problems where a component type is used many times, we can optimize by constructing one Mesh and FiniteElementSpace per component type. Currently, these are constructed for each instance of the component.
• TopologyHandler::LoadBalance() is written only for simple Cartesian cases and has room for improvement in general

[chldkdtn]

I guess the failing test is because libROM PR #316 has not been merged yet, right?