At start of timestep, if time is a multiple of shelficeremeshfrequencey, call
shelfice remeshing.

Shelfice_Remeshing calls the following subroutines in turn. Subroutines with JJ
have been modified, those without are at present unmodified.


INI_MASKS_ETC_JJ - Ro_surf set to 0, otherwise causes issues with
                   shelfice_update_masks

                   CALL SHELFICE_UPDATE_MASKS_JJ

                   Set hFacs to 1 or 0. Set h0Facs. Generate masks. Generate
                   ksurfs

                   Mask U and V velocities on ice boundaries resulting from 
                   remeshing

SHELFICE_UPDATE_MASKS_JJ - Called from within INI_MASKS_JJ
                           Comment out initialising R_shelfice

                    Main Remesh Loop. IF etaN is > SHELFICESplitThreshold, or
                    < SHELFICEMergeThreshold then the following variables are
                    updated 
 
                    etaN, etaH, etaHnm1, R_shelfice, uVel, vVel,gvnm1, gunm1,
                    salt, theta, hFac_surfC, hFac_surfnm1C

                    hFacs of 1 and 0 updated to reflect shelfice extent.

OBCS_INIT_FIXED - Corrects MaskIn to allow for Obcs

INI_LINEAR_PHISURF -initialise Bo_surf and phisurf

INI_CG2D         - initialise CG variables

CALC_SURF_DR      - Calculate hFac_surfs and hFac_surfw from hFac_surfc
CALC_SURF_DR     - Called 2nd time to update hfac_surfnm1

UPDATE_SURF_DR  - update hFacs based on hFac_surfs

UPDATE_CG2D       - update CG variable based on hFacs

UPDATE_SURF_DR  - update hFacs based on hFac_surfs

INTEGR_CONTINUITY - Generate Wvel based on Uvel and Vvel