CMake configuration cleanup

[wrtobin]

The current CMakeLists.txt needs to be cleaned up and made to reflect current CMake best practices.

Our methods of finding and specifying dependencies need some work, and we need to break the configuration down into separate per-directory CMakelists.txt instead a single monolithic configuration file.

[cwsmith]

So far, I've found that
https://github.com/SCOREC/msi/blob/fusion/cmake/FindHdf5.cmake
and
https://github.com/SCOREC/msi/blob/fusion/cmake/FindPetsc.cmake
will fail cmake (FATAL_ERROR) if libraries or headers are missing. They should not fail, the CMakeLists.txt that calls them should decide if what they found meets the requirements.

I've started some cleanup here:
https://github.com/SCOREC/msi/tree/cws/cmake_cleanup