TableSort: better support for thead [Closes #348]

Author: dg

src/Tracy/TableSort/table-sort.css

@@ -2,11 +2,11 @@
  * This file is part of the Tracy (https://tracy.nette.org)
  */
 
-.tracy-sortable tr:first-child > * {
+.tracy-sortable > :first-child > tr:first-child > * {
 	position: relative;
 }
 
-.tracy-sortable tr:first-child > *:hover:before {
+.tracy-sortable > :first-child > tr:first-child > *:hover:before {
 	position: absolute;
 	right: .3em;
 	content: "\21C5";

src/Tracy/TableSort/table-sort.js

@@ -11,7 +11,7 @@
 	{
 		static init() {
 			document.documentElement.addEventListener('click', (e) => {
-				if (e.target.matches('.tracy-sortable tr:first-child *')) {
+				if (e.target.matches('.tracy-sortable > :first-child > tr:first-child *')) {
 					TableSort.sort(e.target.closest('td,th'));
 				}
 			});