namelist update in new 4.0.6 branch

[jdha]

[jdha]

first stab made at namelist_cfg

TODO: namelist_ref (as there are a few additions via MY_SRC e.g. ln_reset_ts, sn_dep, sn_msk and ln_tsd_interp)

[atb299]

sn_dep, sn_msk not in namelist_ref. Should they be?