Change the way to address login form

Access the login form via its property "id" instead of its (changing) position, as it's not possible to use its name (this form has no name)

recipes/mediapart.recipe

@@ -144,10 +144,12 @@ def print_version(self, url):
 
 # -- Handle login
     def get_browser(self):
+        def is_form_login(form):
+            return "id" in form.attrs and form.attrs['id'] == "logFormEl"
         br = BasicNewsRecipe.get_browser(self)
         if self.username is not None and self.password is not None:
             br.open('https://www.mediapart.fr/login')
-            br.select_form(nr=2)
+            br.select_form(predicate=is_form_login)
             br['name'] = self.username
             br['password'] = self.password
             br.submit()