Banking improvements

Fixes : 
 - Partial_reconcile field.
 - _find_commercial_parent to match same partner on completion.
 - Invoice generation dates are now the same as the original move_line/statement_line one.

Adds :
 - Completion rule based on old move lines.
 - Invoice BVR ref is now propagated in move.ref to make the manual reconciliation process easier.
 - Reconciliation with writeoff in a fund.