set maxlength attribute on inputs if present in validation

If a field has a maximum length set in the javascript validation then
add a maxlength attribute so the user doesn't have to wait till
submission to find out about it.

web/cobrands/fixmystreet/fixmystreet.js

@@ -446,6 +446,11 @@ $.extend(fixmystreet.set_up, {
             var $el = $('#form_' + name);
             if ($el.length) {
                 $el.rules('add', rule);
+                if (rule.maxlength) {
+                  $el.attr('maxlength', rule.maxlength);
+                } else {
+                  $el.removeAttr('maxlength');
+                }
             }
         });
   },