fix(finance): add IExpense

ts/finance/expense.ts

@@ -0,0 +1,6 @@
+import { IInvoice } from './invoice';
+
+export interface IExpense {
+  invoice: IInvoice,
+  account: string
+}

ts/finance/invoice.ts

@@ -0,0 +1,18 @@
+import { IContact } from '..';
+
+export type TInvoiceStatus = 'draft' | 'invoice' | 'paid' | 'refunded';
+
+export interface IInvoiceItem {
+  name: string;
+  unitType: string;
+  quantity: number;
+  vatPercentage: number;
+}
+
+export interface IInvoice {
+  pdfFile?: any;
+  billedBy: IContact;
+  billedTo: IContact;
+  status: TInvoiceStatus;
+  items: IInvoiceItem[];
+}