Feature: json error

[sarrala]

Would be nice to have something like:

$result = json_encode($response);
if (json_last_error() != JSON_ERROR_NONE) {
    return json_encode(['error' => json_last_error_msg()]);
}
return $result;

@ AjaxView::render

What do you think about it?

[dereuromark]

If you can make a pr go for it.

[sarrala]

PR created.