Sorts a structured array by '#title' property.
Callback for uasort() within:
$a: First item for comparison. The compared items should be associative arrays that optionally include a '#title' key.
$b: Second item for comparison.
function element_sort_by_title($a, $b) {
$a_title = is_array($a) && isset($a['#title']) ? $a['#title'] : '';
$b_title = is_array($b) && isset($b['#title']) ? $b['#title'] : '';
return strnatcasecmp($a_title, $b_title);
}