fix: BAC-29 Implement Mappers for Common Classes (#101)

Reviewed-on: #101
Co-authored-by: Janis <janis.e.20@gmx.de>
Co-committed-by: Janis <janis.e.20@gmx.de>

knockoutwhistweb/app/dto/UserDTO.scala

@@ -0,0 +1,19 @@
+package dto
+
+import model.users.User
+import play.api.libs.json.{Json, OFormat}
+
+case class UserDTO(id: String, username: String)
+
+object UserDTO {
+
+  implicit val userFormat: OFormat[UserDTO] = Json.format[UserDTO]
+
+  def apply(user: User): UserDTO = {
+    UserDTO(
+      id = user.id.toString,
+      username = user.name
+    )
+  }
+
+}