Code + comment cleanup for the response models

ref #39

src/models/responses/ResponsePrincipal.ts

@@ -4,16 +4,20 @@ import {
 import { Principal } from '../entities/Principal';
 
 /**
- * Defines Principal's response class.
+ * Defines the principal response.
 */
 export abstract class ResponsePrincipal {
 
     /**
-     * Autogenerated unique id (primary key).
+     * The principal's id.
      */
     @IsInt()
     id: number;
 
+    /**
+     * Creates a ResponsePrincipal object from a principal.
+     * @param principal The principal the response shall be build for.
+     */
     public constructor(principal: Principal) {
         this.id = principal.id;
     }