[REF] sale: portal: factorize some portal code to ease future additions
[REF] sale: portal: factorize some portal code to ease future additions

 * get order access right check in its own method. Purpose is to allow
   its use in other methods and avoid writing same code several times;
 * factorize order customer view values computation. Purpose is to allow
   adding values when displaying the page through inheritance. For example
   to add available payment means in sale_payment.

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