Implement search for Event

This is to offer the search in the Events page
@jogwen I can't just plug in in your because you don't use a queryset for your class, but you create an ad_hoc participant_list on the context.

You can either go done the standard queryset way, or add one more variable in the context (and update the template as well)

It's your call, so I'll leave it for now and you can integrate it the way you want.

I also leave #15 (Search) open