wip: erp5_accounting: invoice number should be continuous

if use uid IdGenerator, we may have incontinuous invoice number, but it seems it's very important to have continuous one.

the following scenario can reproduce error(in theory):

1. System call this script when user confirm invoice transaction, an invoice number is generated by portal_ids.generateNewId
2. If somehow this script ends with database conflit error
3. This script is called again, a new invoice number is geneated again

And uid IdGenerator use non_continuous_integer_increasing, there has no guarantee for continuous