GSA doesn't like null values in data.json files (revise output and amend validator)
the references field is an array, store it space-separated like we do with programCode and bureauCode, and on generating data.json files do a split on spaces
granularity is no longer in the POD schema since 1.0
add new 'overrides' harvester config, and refactor/simplify the data.json import code
add a new config option to exclude datasets by exact values of fields or regular expressions