Code cleanup and refactoring before starting on subgridvalidator.

- Moved zoltanIntegration.cpp::MPIConfig into a proper class in
mpiutils.cpp
- Created mpiutils.cpp and move definitions from header file and into
src-file.
- Wrote Doxygen documentation for functions in mpiutils.
Added scaffolding for subgridvalidator program.

- Created stub main-function.
- Added to CMakeLists.txt.
Header file cleanups.

- Turn off warnings in <oltan_cpp.h> using pragmas.
- Move includes from mpiutils.hpp into mpiutils.cpp.
Added mpiutils::getMPISize

- Analogous function to getMPIRank to get the number of MPI-nodes.
Remember to initializeZoltan in RuntimeMPI::ctor.
subGridValidator now checks all aspects except
UnstructuredGrid::face_cell
Added SubGrid::global_face member.

- Needed to setup the face_cells mapping in SubGridBuilder.
Build face_cells for SubGrids.

- Added Boundary enum.
- SubGridBuilder now builds UnstructuredGrid::face_cells for subgrids.
Documentation cleanups.
Merge branch 'master' of https://github.com/sintefmath/equelle