[ticket/11795] Get rid of pagination JS variables

Move pagination variables to data attributes
Replace A_BASE_URL with BASE_URL and use TWIG to escape it

PHPBB3-11795

phpBB/styles/subsilver2/template/overall_header.html

@@ -41,7 +41,7 @@ function jumpto()
 {
 	var page = prompt('{LA_JUMP_PAGE}{L_COLON}', '{ON_PAGE}');
 	var per_page = '{PER_PAGE}';
-	var base_url = '{A_BASE_URL}';
+	var base_url = '{{ BASE_URL|e('js') }}';
 
 	if (page !== null && !isNaN(page) && page == Math.floor(page) && page > 0)
 	{