Add a warning that the Link in the email deletes the signup

Created by: lujobi

The students still seem to be quite used to the concept of the old system. We received some emails of people accidentally deleting their submission. We were asked for a "two stage" deletion with confirmation on the website but i think this is above our current capacities since we have to concentrate on the transition to VSETHs infrastructure.

Maybe a bolt warning (that clicking on this link will immediately delete their signup) above the link could help to prevent that. At least until people are used to the new system.