Account migration

End of @alexis-via's work. See #24
Hi @alhashash, 
As I see in V7, account_id is present in account.bank.statement.line model. (and Finally present in V8 as you said)
Ref: https://github.com/odoo/odoo/blob/7.0/addons/account/account_bank_statement.py#L560
So I guess that there is "nothing to do".
Can you detail your point of you ?
Regards.