DECODR1401s NH4 zeroing

Since there may be some usefulness in keeping the ability of auto-datacoding-4 non-zero, deep, offshore ammonia, it is now an option. Next to the NH4 parameters of the nutrient module there is a checkbox labeled "4". If checked, it will datacode 4 non-zero deep offshore ammonia on whichever stations (> 60) are selected - you can run an individual station or subset of stations with this option toggled.

It should be noted that this option only affects the sta.csvs when the update sta.csv box is selected. Also, if the 4 box is unchecked, it will change previously datacoded 4 ammonias back to datacode 0 (but only offshore, non-zero, deep ammonias). Let me know if this is not desired and I can make it keep whatever datacode is present.