dashboard: add option to manager widget to resend email invitations to Uploaders/Reviewers

[GraemeWatt]

Request from Frank Geurts (STAR):

I am the HEPdata coordinator for STAR. Over the past years I have come to realize that it would be really nice to have a feature that would allow me to resend the automated emails that usually are send when an uploader and reviewer are assigned.

I am not sure such a “resend invitation” option exists, but if it does then please point me to it. If it does not exists I think this would be a very welcome addition that will help send such reminders or (more often) address issues where the uploader/reviewer lost (read: deleted) the original email.