PaymentTransaction_getTotalPayablePrice returns negative value.

Make it sure that lines are always separated (split_on_line).
Took movements only from same invoice (first_causality_on_delivery).

invoice_2 is not updated.

Movements where cloned w/o resetting its delivery value.

For invoice transaction builder add model lines.
Check that only one simulation movement is delivered to one line.

Never aggregate lines (split_on_line).
Find proper invoice (first_causality_on_delivery).
Avoid setting not needed categories (specialise and causality).

Also fixup naming.

Builder is used to create one and only one invoice.

Also declare other tests and avoid code duplication.