Implemented address validation as designed by trytond-shipping
Merge pull request #47 from tarunbhardwaj/address_validation

Implemented address validation as designed by trytond-shipping
Released version 3.2.1.5
Merge branch 'release/3.2.1.5' into develop
Fix for error occuring on selecting carrier. #6456

  * When a shipment is created from scratch, and a carrier is selected,
`on_change_carrier()` leads to `get_ups_shipping_cost()`, which should
ideally not be called as there are no values yet inside our unsaved
shipment.

  * In `get_sale_price()`, the fix is to check that the given shipment
ID is a positive integer. This indicates a saved shipment.
Added decorators to some methods. #6456