Unite code for handling listed pairs

Some implementation details are closer to the other listed
interactions than the group-kernel non-bondeds. This functionality
will also survive the death of the group kernels, so may as well be
separated now.

This is pure code motion, to prepare for transition to the
listed-forces module.

Had to add an #include guard to a not-really-related file.

Some not-quite related clean-up in nonbonded.h

Added temporary cycle suppression until this moves into the
listed-forces module

Change-Id: Ie8865f5ca1a4512d75e70e4b7f25b90f6ed019ec