[FIX] hr_expense: fallback on domain if no analytic_account for line_ids
[FIX] procurement: background procurement scheduler should be working in batch mode, with one transaction per order

A programming error during an older refactoring lead to
the scheduler working with a single monolithic transaction.
This could cause unnecessary resource contention, plus
undesired rollback of all previous operations in the event
of an exception during scheduling.