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/event.ex

@@ -61,6 +61,7 @@ defmodule MobilizonWeb.Schema.EventType do
       arg(:page, :integer, default_value: 1)
       arg(:limit, :integer, default_value: 10)
       arg(:roles, :string, default_value: "")
+      arg(:actor_id, :id)
       resolve(&Event.list_participants_for_event/3)
     end