Extended Invoice to have "sent on" field that holds the date information of when the last email notification was sent to customer, either manually or by process.

Client tier modifications:
Modified following jsp pages: invoice/viewBody.jsp

Descriptors:
- application resources updated.
		
Server tier modifications:

Updated classes:
 com.sapienter.jbilling.server.notification.NotificationSessionBean()
 com.sapienter.jbilling.server.process.BillingProcessSessionBean
 com.sapienter.jbilling.server.invoice.InvoiceWS
 com.sapienter.jbilling.server.invoice.InvoiceBL
 com.sapienter.jbilling.server.invoice.db.InvoiceDTO

Database tier modifications: 

-- Invoice sent date added to table
ALTER TABLE `invoice` ADD COLUMN `sent_on` DATETIME AFTER `last_reminder`;
added new JBilling API getCompany() and updateCompany()