task/ta-npe-001-02 -- translate raw Service Code

nparcel/loader.py
* updated the FIELDS global to include a callback option under the
  "Service Code" value
* new method translate_service_code()  to translate postcode
  information to state

nparcel/table/__init__.py
* updated the insert_sql() method handle the 'NULL' string during
  inserts
task/ta-npe-001-03 -- introduce new primaryelect.py module structure