Implemented the second round of the toResponse normalisationf for all classes

ref #67

src/models/entities/Participant.ts

@@ -9,6 +9,7 @@ import {
 } from "class-validator";
 import { Column, Entity, ManyToOne, PrimaryGeneratedColumn, TableInheritance } from "typeorm";
 import { config } from '../../config';
+import { ResponseParticipant } from '../responses/ResponseParticipant';
 import { Address } from "./Address";
 import { IAddressUser } from './IAddressUser';
 
@@ -74,4 +75,9 @@ export abstract class Participant implements IAddressUser {
   @IsOptional()
   @IsEmail()
   email?: string;
+
+  /**
+   * Turns this entity into it's response class.
+   */
+  public abstract toResponse(): ResponseParticipant;
 }