Export and Import Attendees

Adds two functions to export and import all attendees in the database. Will be super-useful for data entry as well as integration with a CSV.

Bonus: Works dynamically - unless we add a new type of column, this requires no management.

Still to do: Foreign keys are just exported and imported as-is. AC doesn't need this to work, but obviously we should figure out sane special-casing later.
BTW, this for loop is from the example script I sent, and the reason why it selects all Attendees who have a first name is to filter out unclaimed group badges.  It's entirely possible that you WANT your export script to include unclaimed group badges, in which case you should change this.  Also there's not currently an ``order_by`` callm so this whole thing is unordered.