[ticket/17151] Improve radio input type handling

- allow more than 2 buttons count
- allow custom buttons order
- allow custom button labels

Implemented by allowing JSON data format, backward compatibility preserved.

PHPBB3-17151

phpBB/styles/all/template/macros/forms/radio_buttons.twig

@@ -1,2 +1,3 @@
-<label>{{ FormsInput(FIRST_BUTTON) ~ FIRST_BUTTON_LABEL }}</label>
-<label>{{ FormsInput(SECOND_BUTTON) ~ SECOND_BUTTON_LABEL }}</label>
+{% for button in BUTTONS %}
+<label>{{ FormsInput(button) ~ button.label }}</label>
+{% endfor %}