Editing Same as shipping logic

=== Prerequisites ===

The Recipient and Sender are linked to a User, if any. A user may have more than one Recipient / Sender. Why this is important? In the checkout process there are two scenarios: 

# Guest checkout
# Logged-in checkout

==== 1. Guest checkout ==== 

In this scenario when editing the Recipient / Sender details they are always overwritten. In other words, a Guest checkout will have one Recipient and one Sender object. These Recipient and Sender are not linked to a User. 

==== 2. Logged-in checkout ==== 

In this scenario the customer has two options: ''Add a new address'' and ''List previously saved addresses''.  With ''Add a new address'' a new Recipient / Sender is created in db and linked to the Checkout. When picking a ''previously saved address'' a different Recipient / Sender is linked to the Checkout. 


== The same as shipping workflow == 
When choosing the Billing Address (Sender) the Customer has 2 options:

* Same as shipping address
* Add new billing address

=== Same as shipping address ===

With this no Sender is created in db, but a flag is marked. As a result upon checkout completion a Sender will be created and attached to the Order. 

NOTE: Recipient fields must match Sender's. Results that Recipient must have Company and Company VAT fields.

=== Add new billing address === 

In this case the ''same_as_shipping'' flag is set to false (0) and a new Sender is created and added to the Checkout. 

==== Dealing with  ====