Fix constants, units and conversion factors
Pressure definition was wrong, should be in bar. There's no point in
giving a standard conversion factor to other units that nobody uses.
Giving the "accuracy" of various quantities is useless without
specifying what the value in parentheses means. We make no use of
those accuracy values anywhere in the code. We should cite the source
and leave it up to the user with some potentially more accurate value
to decide if their value, with _its_ error, is close enough to the
value used in GROMACS to be acceptable.
Change-Id: I417873db5ab01aa53ad409988eb738442f2f0305