Update suite to a more standard PD control

[MartinDix]

Present suite is based on Met Office AMIP configuration so has time varying GHG and aerosol. Should switch to the CM2 PD control configuration which used ~ year 2000 average values.

[MartinDix]

• Add the iceberg melt flux that matches snow accumulation to get water conservation.
• UM netCDF conversion

[MartinDix]

Switch to a PI control instead? Perhaps when we start using CABLE?