[FIX] account: another way to resolve multi currency reconciliation on bank statement...

[FIX] account: another way to resolve multi currency reconciliation on bank statements: show the amount in statement line currency instead of converting them into the statement currency. This is needed in order to have a balance of 0 in the foreign currency. The only remaining thing is to make a foreign currency exchange writeoff automatic at the reconciliation time if we reconcile 2 lines having the same currency_id