Refactor code in order to be compatible with fiscal position rule module

[sebastienbeau]

Partner and address must be set correctly before calling the onchange method.
With this refactor and this other PR OCA/connector-ecommerce#7, the fiscal position are set correctly on sale order when importing a sale order

[coveralls]

Coverage decreased (-0.04%) when pulling de2d8e5 on akretion:7.0_add_position_fiscal_compatibility into 4b04b9c on OCA:7.0.

[guewen]

I was sure it was already working, anyway the code is better know I think, using the options of the mapper.

Thanks

👍

[sebastienbeau]

A case that was not working was the case where you create a customer with a Suisse address as main address and send the delivery to France.
In this case the address used for setting the fiscal position will be the suisse one and not the french one (In France fiscal position are based on delivery address).

[bguillot]

Thanks

👍

[florian-dacosta]

👍