Consistent maximum lengths for DataImport creation

Closes #653 (closed)

• The DataImport.best_class CharField is updated to not exceed 36 characters because it is either a boolean as a string ("True" or "False"), or a UUID: len(str(uuid4())) == 36.
• The DataImport.name_contains CharField can now go up to 250 characters because the Element.name field has a length of 250 characters.
• The process_name, name and type serializer fields on CreateElementsWorkflow are updated to include
• There were no unit tests for process_name at all.