Extract User from Actors context

Mobilizon.Actors.User -> Mobilizon.Users.User
Also Mobilizon.Actors.Service now become Mobilizon.User.Service
And Mobilizon.Users and Mobilizon.UsersTest is introduced.

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

lib/mobilizon_web/resolvers/event.ex

@@ -4,7 +4,8 @@ defmodule MobilizonWeb.Resolvers.Event do
   """
   alias Mobilizon.Activity
   alias Mobilizon.Events.{Event, Participant}
-  alias Mobilizon.Actors.{User, Actor}
+  alias Mobilizon.Actors.Actor
+  alias Mobilizon.Users.User
 
   # We limit the max number of events that can be retrieved
   @event_max_limit 100