Reverted to id based relation setter

ref #13

src/errors/GroupContactErrors.ts

@@ -6,7 +6,7 @@ export class GroupContactWrongTypeError extends NotAcceptableError {
 	name = "GroupContactWrongTypeError"
 
 	@IsString()
-	message = "The groupContact must be either a existing groupContact, new groupContact or a existing adress's id. \n You provided a object of another type."
+	message = "The groupContact must be an existing groupContact's id. \n You provided a object of another type."
 }
 
 export class GroupContactNotFoundError extends NotFoundError {