Improve overall configuration and support

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

lib/service/email_checker.ex

@@ -0,0 +1,15 @@
+defmodule Mobilizon.Service.EmailChecker do
+  @moduledoc """
+  Provides a function to test emails against a "not so bad" regex
+  """
+
+  @email_regex ~r/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/
+
+  @doc """
+  Returns whether the email is valid
+  """
+  @spec valid?(String.t()) :: boolean()
+  def valid?(email) do
+    email =~ @email_regex
+  end
+end