Transform all Adminer selects into select2 (for filtering)

adminer-select2.php

<?php

class AdminerSelect2
{
    function head() {
    ?>
<link href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.2.4/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"></script>
<script>
jQuery(document).ready(function($) {
    initSelect2();
    jQuery('legend a').on('click', function(e) {
        initSelect2();
    });
});
function initSelect2() { jQuery('select').select2(); }
</script>
<?php
    }
}