Each time we start the checkout process, the whole context is created from scratch. Due to that, after editing cart on any checkout step we loose data as the whole operation is triggered by the "Go to checkout" button.

Steps to reproduce:
1. Add some product to the cart.
2. Go to the checkout.
3. Go through e.g. two first steps.
4. Go to "Edit cart".
5. Go to checkout again.

Result:
The data you filled in before is lost.

Expected result:
Given the previous checkout was stored in session, you should see all your choices filled in.