invoicing: invoice transaction builders should find corresponding deliveries only through explanations

What happened before :
- user confirm sale invoice
- activity for building vat invoice lines is created
- user change destination_section
- since builder was expecting having same destination_section on delivery
and simulation movements, it was failing

Now, the builder does not look at source/destination or other categories, it only looks
for common explanation. This can be done this way only because transaction lines should
go inside the same delivery as invoice lines with standard invoicing.