Unify constants

[bderembl]

This is a minor issue but several constants are re-defined in airsea_variable:

   REALTYPE, public, parameter         :: cpw=3985.
   REALTYPE, public, parameter         :: emiss=0.97
   REALTYPE, public, parameter         :: bolz=5.670374419e-8
   REALTYPE, public, parameter         :: kelvin=273.15
   REALTYPE, public, parameter         :: const06=0.62198
   REALTYPE, public, parameter         :: rgas = 287.1    !
   REALTYPE, public, parameter         :: g = 9.81        ! [m/s2]
   REALTYPE, public, parameter         :: rho_0 = 1025.   ! [kg/m3]
   REALTYPE, public, parameter         :: kappa = 0.41    ! von Karman

I see at least cpw, g, rho_0, kappa

[bolding]

You are right - but it seems nobody really has resources to maintain GOTM.

At least I'm behind with two things I've already promised.