Add a dropdown on participate menu, disallow listing participations

Now requires quering the person endpoint to know if an actor
participates in an event, organizers can make authenticated requests to
event { participants { } } to see the pending / approved participants.

Also closes #174

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon_web/schema.ex

@@ -116,7 +116,6 @@ defmodule MobilizonWeb.Schema do
     import_fields(:person_queries)
     import_fields(:group_queries)
     import_fields(:event_queries)
-    import_fields(:participant_queries)
     import_fields(:tag_queries)
     import_fields(:address_queries)
     import_fields(:config_queries)