Had to do a couple of changes to the database: add the currency_code to
the payment relation, to format the price according to the payment’s
currency instead of the company’s; and the reference SQL function, to
replace the equivalent golang function, so that i can use it to index
payments.
The rest is mostly the same as any other page, except that the
individual payment’s page is not a form, but a regular info dump.
I also moved the payment settings as a sub-route of payments, as i
believe this makes more sense than an additional user menu item.
I tried to use ../, and ../../ to make the routes relatives, but it
would not work well because the same page would have two URLs, one
ending with slash and another without, and the relative links would be
different on each case.