Net enthalpy budget diagnostic

[gustavo-marques]

We would like to have a "NET ENTHALPY BUDGET" in the diags.log. For now, it should include all common enthalpy terms accounted for by both ocn and atm, as follows:

	atm	ocn	SUM
hlatvap	XXXXX	XXXXX	XXXXX
hlatfus	XXXXX	XXXXX	XXXXX
hrain	XXXXX	XXXXX	XXXXX
hsnow	XXXXX	XXXXX	XXXXX
hevap	XXXXX	XXXXX	XXXXX
hcond	XXXXX	XXXXX	XXXXX
SUM	XXXXX	XXXXX	YYYYY

These terms should only be computed over ocean points (i.e., they should have * ofrac(n)).
hlatvap and hlatfus are already computed for atm and ocn. The atm values must be modified to only account for ocean points.
Currently, hrain, hsnow, hevap, and hcond are only computed for ocn (see here). Corresponding terms must be introduced for atm (e.g., hrain_atm, hsnow_atm, hevap_atm, and hcond_atm ). These will have a different formulation than the ocn counterparts (exact formulation will be provided in the near future), but for now (implementation phase), they can follow ocn (see here).

The goal is to have the sum of these terms balanced (YYYYY = 0).

cc'ing: @jedwards4b, @PeterHjortLauritzen