fix(core): add ICheckingAccount, IPayment, TCurrency

ts/finance/checkingaccount.ts

@@ -0,0 +1,8 @@
+import { TCurrency } from "./currency";
+import { IPayment } from "./payment";
+
+export interface ICheckingAccount {
+  name: string;
+  currency: TCurrency;
+  payment: IPayment[];
+}

ts/finance/currency.ts

@@ -0,0 +1 @@
+export type TCurrency = 'eur' | 'usd' | 'sek'

ts/finance/payment.ts

@@ -0,0 +1,4 @@
+export interface IPayment {
+  amount: number;
+  date: Date;
+}