change schema before adding node api

add node_relation table
```sql
create table `node_relation` (
    `id` INT UNSIGNED NOT NULL,
    `to` INT UNSIGNED NOT NULL,
    `relation` TINYINT(1) NOT NULL DEFAULT 0, -- 0 for parent_and_child
    `check` TINYINT(1) NOT NULL DEFAULT 0, -- 1 for checked 0 for not
    INDEX (`id`),
    INDEX (`to`)
 ) ENGINE = InnoDB DEFAULT CHARACTER SET utf8;
```