Allow organizers to re-send receipt

[alxblock]

I've had many requests from people to re-send their receipt/ticket, and I'm not able to do so.

This is similar to this request, in that there should simply be a way to send the receipt email again. If it's more difficult to allow for users to resend the receipt themselves, maybe it would be possible to add it into the Admin UI, so that WordCamp Organizers can send them when there's a request.

[iandunn]

Asked the Community Team for approval/feedback at https://make.wordpress.org/community/2015/11/02/approval-for-123-camptix/

[alxblock]

When I requested this, I had in mind that it would be a text link in the Attendee Information table, when you click through to Edit an Attendee.

It could be a simple and firing off the same initial email with the receipt information. Since that receipt should only be sent to the email address on file for the purchase, I don't think that there's any need to have the email address be editable.

Here's a simple idea for placement:

[iandunn]

The team approved this, so now it just needs a pull request.