/**
  * Returns all categories available
  * 
  * @return array 
  */
 public static function getAll()
 {
     if (self::$_items === NULL) {
         self::$_items = array();
         if ($items = TBGListTypesTable::getTable()->getAllByItemType(self::CATEGORY)) {
             foreach ($items as $row_id => $row) {
                 self::$_items[$row_id] = TBGContext::factory()->TBGCategory($row_id, $row);
             }
         }
     }
     return self::$_items;
 }