allow organizers to create an event that is not a class

I really want to use Bridge Troll for our "work day" on March 14th, so we can see ahead of time which volunteers have experience as teachers or organizers.

I also think it would be good for study sessions without a specific curriculum (where it is also helpful to know how people have been involved in the community before).   I believe Bridge Troll could be a powerful tool to strengthening relationships within our community if used in this way.

I think we used to be able to make an event without having to specify a type of class, but now it looks like that is required.  It also means that if you want to test out a new curriculum, you need to add it for everyone.

Maybe the popup field for the class could have an optional text field instead