add datetime to the meeting attendance lists

[JoeJasinski]

As a venue and chipy organizer, I want to know when people register for a meeting, so that I can more easily track who is added to an attendance list over time (especially when sending out updated copies of a list to a venue).

On the meeting detail page in the admin, we currently have a "host registrations" and "private registrations" links, which generate a csv report. We should add the registration time to those csv reports, so that we can determine when people registered. Often times, we'll send updated attendance sheets to a venue, and that field will help determine who has been added between copies.

AC

• Display the a users registration datetime on the "host registrations" and "private registrations" csv report.

[JoeJasinski]

This MR should address this

#531