job-order-list-view: Override delete-activated signal

Delete the job orders selected when this signal is emitted.
purchase-order-list-view: Override delete-activated signal

Delete the purchase orders selected when this signal is emitted.
invoice-list-view: Override delete-activated signal

Delete the invoices selected when this signal is emitted.
job-order-list-view: Call overrided method in new-activated

Not that important, just to make sure this will not get forgotten in the
future.
purchase-order-list-view: Call overrided method in new-activated

Not that important, just to make sure this will not get forgotten in the
future.
invoice-list-view: Call overrided method in new-activated

Not that important, just to make sure this will not get forgotten in the
future.
WIP