Make quantization meet CF compliance

[mauzey1]

Resolves #765

CMOR will now only apply quantization to the dataset variable and not the axes, zfactors, or grids. When quantization is applied, the variable quantization_info will be created in the netCDF file that will contain the quantization algorithm used (bitgroom, bitround, and granular_bitround) and the libnetcdf library version. The dataset variable will now have the attribute quantization_nsb or quantization_nsd depending on the algorithm used.

@durack1 @taylor13 @czender