Add nbnxm kernel benchmark tool

Add nbnxm kernel benchmark tool

This change adds a tool for benchmarking nearly all different
flavors of the Nbnxm non-bonded kernels. The tools uses prepared
coordinate input, to minimize the dependencies on the GROMACS
code base. Currently some there are some minor mdlib and ewald
dependencies beyond the Nbnxm dependency.

Also adds basic end-to-end test.

TODO: Make this tool a separate target with minimal dependencies
      on the rest of GROMACS.

Change-Id: Id9b31ccf9f372af873e08c5dd2b97fb8e5df6eef