Resolve "Return of liquidated liquidations" + Fix liquidation naming issues

Closes #219 (closed)

• Process negative line in liquidations to return the products and adjust stock quantities.
• If liquidation total is negative it will create RINV instead of INV.
• Check for same product in different lines.
• Fix issue with naming on liquidations (Albarán de devolución).
• New compute field is_liq_return for RLIQ (Devoluciones de deposito only) used to filter.
• Now RLIQ are not visible on "Facturas rectificativas".
• Only RLIQ are visible on "Devoluciones de deposito".
• Fix issue when creating rectificative invoice from liquidation is_liquicacion = True