Fixes #1625 adds class to body

Adds class to body, get id for category tag or picture, add dynamic class to body using id
Also used on page where albums and tags are combined

TODO make compatible with modus

include/page_header.php

@@ -47,6 +47,10 @@ $template->assign(
     'LEVEL_SEPARATOR' => $conf['level_separator'],
 
     'SHOW_MOBILE_APP_BANNER' => $show_mobile_app_banner,
+
+    'BODY_CLASS' =>
+      isset($page['body_class']) ?
+        $page['body_class'] : '',
     ));