Import attendees

[mwithheld]

In issue #65 we got the ability to export a list of attendees from single session. It would be useful to be able to import this same list into another session, for example to move attendees between sessions or import from some external system.

I propose one of the following two options:

• Add an icon for Excel/CSV import of attendees for each of the listed sessions in the View All Sessions page; or
• Add to the "Attendees" page to import an Excel/CSV list of attendees for that single session. This would be added to the existing options which include Take Attendance, Add/Remove Attendees and Go Back.

I recognize this is unlikely to happen without funding, but thought it'd be good to have an open request.