Moved random number generator code to separate dir.

GROMACS sports two random number generators for historical
reason. The oldest one is phased out in this patch.
Changing the random number
generator means that e.g. replica exchange simulations will
not be reproducible (if they ever were in practice).

Change-Id: If24f1019fba9b9412713b5fe04b5c0a8a7638468