Add hidden form to re-post AJAX requests

Serializing the search box form is bad, because the AJAX thing submit
any changes that the user makes to the contents of the box. This results
in unexpected behaviour.

tests/app/main/views/test_activity.py

@@ -193,7 +193,11 @@ def test_search_recipient_form(
     query_dict = parse_qs(url.query)
     assert query_dict == {}
 
-    assert page.find("input", {'name': 'to'})['value'] == expected_search_box_contents
+    recipient_inputs = page.select("input[name=to]")
+    assert(len(recipient_inputs) == 2)
+
+    for field in recipient_inputs:
+        assert field['value'] == expected_search_box_contents
 
 
 def test_should_show_notifications_for_a_service_with_next_previous(