Version 1.5.1 update tags multilingue

Ajout du multilingue pour les tags.

Modification de la bdd :

ALTER TABLE `prefix_tag` ADD `lang` VARCHAR(8) NOT NULL DEFAULT 'fr' AFTER `zone`;
ALTER TABLE `prefix_tag` DROP PRIMARY KEY, ADD PRIMARY KEY (`id`, `zone`, `lang`, `encode`);
ALTER TABLE `prefix_tag` DROP INDEX `type`, ADD INDEX `zone` (`zone`, `lang`, `encode`);