Allow disabling registration, add Interactive module with tools

lib/sso_bsn/accounts.ex

@@ -60,6 +60,7 @@ defmodule SsoBsn.Accounts do
 
   """
   def register_user(attrs) do
+    if not Application.get_env(:sso_bsn, :enable_registration, false), do: raise "Cannot register a user: disabled"
     %User{}
     |> User.registration_changeset(attrs)
     |> Repo.insert()