Ensure directory containing extract.py is on sys.path for scenarios where extract.py is executed from another location
Added unique attribute to FieldDefinition class.
Generate Data Template using Data Model.
Implemented SQLAlchemy Init
Modified structure of StorageRecord class
Changed structure of StorageRecord, adding columns for data_model JSON and data_item_metadata JSON.
Documented plugin class.
Implemented basic versioned storage logic.
Fixed dependent import of PostProcessedDataItem in validation.py
Fixed exec statement syntax for compatibility with Python 2.x rather than Python 3.x