Restrict users so they can't register for two events happening at the same time

[juniwbjerde]

As LEGO is now there are no restrictions for registrations on a event that depends on other events the user has registered for.

It would be nice if we added a restriction so that no user could register for a event if they have already registered for another event happening at the same time. This is because:

• We've had a specific case where a company had two courses planned for the same time one day and wanted users only be be allowed to register for one of the two courses. This had to be solved by manually making sure that no one registered for both courses.
• Generally it does not make sense to have a user registered for two events at the same time. They cannot be at both events, therefore it should not be allowed so that someone else can have their place at one of the events.

[ivarnakken]

Very cool feature, but I'd like to add that some events span across multiple days, even though they don't require people to attend multiple days Example:

I think a simple warning is better than to restrict entirely.