add CustomError Class as wrapper for "Error"

throw new CustomError('message','errorCode')

server/interfaces.ts

@@ -9,3 +9,21 @@ export interface localized_string {
 		[k in supported_languages]: string
 	}
 }
+export class CustomError extends Error {
+	private code: string
+	public constructor(message: string, errorCode: string) {
+		super(message)
+		this.code = errorCode
+	}
+	public getCode() { return this.code }
+}
+export const errorCodes = {
+	no_end_date: 'no_end_date',
+	no_string_present: 'no_string_present',
+	no_schedule: 'no_schedule',
+	schedule_not_supported: 'schedule_not_supported',
+	no_repetition_amount: 'no_repetition_amount',
+	invalid_repetition_string: 'invalid_repetition_string',
+	no_creator_id: "no_creator_id",
+
+}