added services and interfaces for expense types

src/app/components/expense-list/expense-list.ts

@@ -11,6 +11,8 @@ export class ExpenseList implements OnInit {
   public constructor(private readonly expenses: Expenses) { }
 
   public ngOnInit() {
-    void this.expenses.getExpenses();
+    this.expenses.getExpenses().then(expenses => {
+      console.log({ expenses });
+    });
   }
 }