templates/CRM/Timetrack/Form/Task/Invoice.tpl: fixes for cost/unit, and added invoice title, ledger_order_id, ledger_invoice_id.
xml/sql schema changes: invoice/korder ledger_order_id allow 0 default, and not mandatory.
timetrack.php: implement the hook_civicrm_triggerInfo(), so that the korder.created_date gets automatically set to CURRENT_TIMESTAMP. Based on civicrm_contact.