Export participants to different formats

* CSV
* PDF (requires Python dependency `weasyprint`)
* ODS (requires Python dependency `pyexcel_ods3`)

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

test/service/export/participants/common_test.exs

@@ -0,0 +1,28 @@
+defmodule Mobilizon.Service.Export.Participants.CommonTest do
+  use Mobilizon.DataCase, async: true
+
+  import Mobilizon.Factory
+
+  alias Mobilizon.Actors.Actor
+  alias Mobilizon.Service.Export.Participants.Common
+
+  test "convert participants to list items" do
+    participant = insert(:participant)
+    actor = insert(:actor)
+    name = Actor.display_name_and_username(actor)
+    assert [^name, _, ""] = Common.to_list({participant, actor})
+  end
+
+  test "convert participants with metadata to list items" do
+    participant = insert(:participant, metadata: %{message: "a message"})
+    actor = insert(:actor)
+    name = Actor.display_name_and_username(actor)
+    assert [^name, _, "a message"] = Common.to_list({participant, actor})
+  end
+
+  test "convert anonymous participants to list items" do
+    participant = insert(:participant)
+    actor = insert(:actor, domain: nil, preferred_username: "anonymous")
+    assert ["Anonymous participant", _, ""] = Common.to_list({participant, actor})
+  end
+end