changes made in api_invoice.py and api_organization.py.

1.paymentmode value sent to the front end.

2.Wrote code in gkUpgrade to set paymentmode (i.e 2 for 'bank' and 3 for 'cash') to make a database consistent.For this, check whether paymentmode is NULL or Not.then check bankdetails are present or not if bankdetails are not present then set payment mode =3, else set paymentmode=2.

please refer issue #851 at gkwebapp