Add in grid cell level C/N balance checking for FATES?

The grid-cell C/N balance checking is especially useful in the model for making sure transient changes of LULC don't result in mass loss/gain. Since, FATES currently doesn't have transient changes, it doesn't seem to matter if the gridcell level checking is done or not. So right now we have it turned off. But, we should consider bringing it back again especially with LUH2 transient changes, such as in #1077.