[FIX] mail: replace _lt to _t for mailboxes' name

Since mailboxes are added after the rpc 'mail/init_message', the translations
are loaded. Therefore it is not necessary to lazily load the translations.

addons/mail/static/src/js/models/threads/abstract_thread.js

@@ -53,7 +53,7 @@ var AbstractThread = Class.extend({
     /**
      * Get the name of this thread
      *
-     * @returns {string|Object} object for lazy translated names with _lt
+     * @returns {string}
      */
     getName: function () {
         return this._name;
@@ -69,7 +69,7 @@ var AbstractThread = Class.extend({
     /**
      * Returns the title to display in thread window's headers.
      *
-     * @returns {string|Object} the name of the thread by default (see @getName)
+     * @returns {string} the name of the thread by default (see @getName)
      */
     getTitle: function () {
         return this.getName();

addons/mail/static/src/js/services/mail_manager.js

@@ -884,19 +884,19 @@ var MailManager =  AbstractService.extend({
     _initializeMailboxes: function (data) {
         this._addMailbox({
             id: 'inbox',
-            name: _lt("Inbox"),
+            name: _t("Inbox"),
             mailboxCounter: data.needaction_inbox_counter || 0,
         });
         this._addMailbox({
             id: 'starred',
-            name: _lt("Starred"),
+            name: _t("Starred"),
             mailboxCounter: data.starred_counter || 0,
         });
 
         if (data.is_moderator) {
             this._addMailbox({
                 id: 'moderation',
-                name: _lt("Moderate Messages"),
+                name: _t("Moderate Messages"),
                 mailboxCounter: data.moderation_counter || 0,
             });
         }