History fields for vertically-resolved sums of soil C and N, and minor fixes

Add history fields for vertically-resolved sums of SOIL1C, SOIL2C, and SOIL3C for C12, C13, C14, and similarly for N. New fields are SOILC_vr, C13_SOILC_vr, and C14_SOILC_vr, and SOILN_vr. For runs that use the output_bgc usermods, including cmip6 runs, we no longer output 'SOIL1C_vr', 'SOIL1N_vr', 'SOIL2C_vr', 'SOIL2N_vr', 'SOIL3C_vr', 'SOIL3N_vr'; instead we output 'SOILC_vr', 'SOILN_vr', and similarly for C isotopes.

Also minor fixes:

• Output cpl hist files in SSP test (resolves #61)
• Remove FATES-related commented-out code in OzoneMod (this has been moved to #618)