Renamed "Salary Deduction" to "Employee Benefit"

Journal, Purchase and Purchase Return vouchers done!!

Changed the column type of "date" columns from "datetime" to better fit the data.

overlord/src/app/receipt/receipt.component.ts

@@ -227,7 +227,7 @@ export class ReceiptComponent implements OnInit, AfterViewInit, OnDestroy {
   }
 
   save() {
-    this.ser.save(this.getVoucher())
+    this.ser.saveOrUpdate(this.getVoucher())
       .subscribe(
         (result) => {
           this.loadVoucher(result);