provide support for sending congratulatory messages

[mandyWW]

It would lovely to be able to send customised, "well done" messages to students when the complete each phase.

If there is a way to do this without storing email addresses (ie. display at the top of the student's Buggy Server page) that would be ideal.

[davewhiteland]

Displaying messages when logged in ought to be feasible, i.e., entirely internal.

In theory the race server could also send email (you weren't using it at RHUL but it's feasible on servers running with USERS_HAVE_EMAIL set, , but I've been avoiding it because it's a whole new requirement that I've managed without this long... but if we had it then a password reset could be supported too.