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>

lib/web/endpoint.ex

@@ -77,17 +77,6 @@ defmodule Mobilizon.Web.Endpoint do
 
   plug(Plug.MethodOverride)
   plug(Plug.Head)
-
-  # The session will be stored in the cookie and signed,
-  # this means its contents can be read but not tampered with.
-  # Set :encryption_salt if you would also like to encrypt it.
-  plug(
-    Plug.Session,
-    store: :cookie,
-    key: "_mobilizon_key",
-    signing_salt: "F9CCTF22"
-  )
-
   plug(Mobilizon.Web.Router)
 
   @spec websocket_url :: String.t()