Implemented the interface in all responses

refr #132

src/models/responses/ResponsePrincipal.ts

@@ -2,11 +2,19 @@ import {
     IsInt
 } from "class-validator";
 import { Principal } from '../entities/Principal';
+import { ResponseObjectType } from '../enums/ResponseObjectType';
+import { IResponse } from './IResponse';
 
 /**
  * Defines the principal response.
 */
-export abstract class ResponsePrincipal {
+export abstract class ResponsePrincipal implements IResponse {
+
+    /**
+    * The responseType.
+    * This contains the type of class/entity this response contains.
+    */
+    responseType: ResponseObjectType = ResponseObjectType.PRINCIPAL;
 
     /**
      * The principal's id.