[FIX] account: _get_analytic_lines needs the date_invoice

During the conversion of account_invoice.py to the new API, the date_invoice written on the invoice has been moved in the end of the action_move_create method.

But, the method _get_analytic_lines needs it sooner.
[FIX] account_analytic_plans: _convert_ref takes only 1 arg

Since the convert of account_invoice to the new api.
_convert_ref is defined as a staticmethod in account_invoice.py
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32