Add date_create and date_imported to membership data

@DSASanFrancisco/portal-members

I want to start migrating the information about when people attend their first meeting into the membership portal so we can do some data mining. At the very least, we should add the date_created and date_imported to the tables that are created by the code. We can backfill the dates by going through eligibility@dsasf.org emails as well as our membership join date.