With the drop of 'transaction_ref' field on account.move.line in
order to ease the reconcilition using 'ref' on account.move, we
need to import each line from the imported file in different
account.moves.
Remove 'ref' from account.move.line preparation
As 'ref' is related to account.move.ref it is not needed
Fix multi move import
multi_move_import on the parser allows to generate 1 account.move
for each line in the imported file, instead of having all the lines
on the same account.move