Access token field is moved directly in sale module. Indeed future commits
will improve customer portal and access tokens will be used in other module
than website_quote. This commit already moves the field.
Moreover some strange code in website_sale already uses access_token even
if it does not exist in that module. Moving the field solves that issue.
Finally so_token defined in stripe is renamed to access_token to have the
same naming through all addons.
Thibault Delavallée
b5146643b5