Add slugs for Posts, Boards and OAuths (#321)

app/javascript/interfaces/json/IBoard.ts

@@ -2,6 +2,7 @@ interface IBoardJSON {
   id: number;
   name: string;
   description?: string;
+  slug?: string;
 }
 
 export default IBoardJSON;

app/javascript/interfaces/json/IPost.ts

@@ -1,6 +1,7 @@
 interface IPostJSON {
   id: number;
   title: string;
+  slug?: string;
   description?: string;
   board_id: number;
   post_status_id?: number;