Make it clear that someone was added from the waiting list in the email

[ravicious]

We sent a bunch of additional invitations yesterday. One person replied that they are not sure if they indeed got a spot at the event or if they got the email by mistake, especially since previously they got an email saying that they didn't make it.

We should make it more clear in the bad news email that they might get invited anyway and also additional invitations should have a bit different copy so that the invitees don't have doubts as this one had.

Might be good to implement this after #154.