[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/adm/style/overall_header.html

@@ -12,7 +12,7 @@
 var jump_page = '{LA_JUMP_PAGE}{L_COLON}';
 var on_page = '{ON_PAGE}';
 var per_page = '{PER_PAGE}';
-var base_url = '{A_BASE_URL}';
+var base_url = '{{ BASE_URL|e('js') }}';
 
 var menu_state = 'shown';