[feature/attachment-management-no-reassignment] Further feature adjustments.

-add database update entry;
- add files statistics checks;
- improve files deletion procedure;
- improve reversed order for pagination;
- adjust template file;
- add missing comma for orphan key in info module;
- change module mode name;
- fix module explanation text;
- add files comments output;
- change attachments per page amount from posts to topics per page value.

PHPBB3-9721

phpBB/install/database_update.php

@@ -1958,6 +1958,13 @@ function change_database_data(&$no_updates, $version)
 					'auth'		=> 'acl_a_group',
 					'cat'		=> 'ACP_GROUPS',
 				),
+				'manage'	=> array(
+					'base'		=> 'attachments',
+					'class'		=> 'acp',
+					'title'		=> 'ACP_MANAGE_ATTACHMENTS',
+					'auth'		=> 'acl_a_attach',
+					'cat'		=> 'ACP_ATTACHMENTS',
+				),
 			);
 
 			_add_modules($modules_to_install);