feat: bank details on the Sales Invoice print in the document's language

Bank Account.account_name and Bank.bank_name are translatable (the Link
field Bank Account.bank cannot be; the Bank's name is what prints), and the
Sales Invoice format renders both through _().

README.md

@@ -29,7 +29,9 @@ show the company's and the party's address in the document's print language (the
 address is re-rendered at print time; party addresses are re-rendered from the linked
 Address instead of printing the stored `address_display`). The withholding tax certificate
 always takes the Thai translation. Translations are keyed on the exact text, so one
-translation of a city or province serves every address that uses it.
+translation of a city or province serves every address that uses it. The same goes for
+the bank details on the Sales Invoice: *Account Name* on the Bank Account and *Bank Name*
+on the Bank are translatable.
 
 ### Withholding tax certificate