feature #534, modernize admin home

* convert the big button "Quick Local Sync" into a simpler action link
* simplify the "quick sync" as a specific action on site_update.php

admin/intro.php

@@ -210,6 +210,7 @@ $template->assign(
     'NB_PLUGINS' => count($pwg_loaded_plugins),
     'STORAGE_USED' => l10n('%sGB', number_format($disk_usage/(1024*1024), 1)),
     'U_CHECK_UPGRADE' => PHPWG_ROOT_PATH.'admin.php?action=check_upgrade',
+    'U_QUICK_SYNC' => PHPWG_ROOT_PATH.'admin.php?page=site_update&site=1&quick_sync=1&pwg_token='.get_pwg_token(),
     )
   );