Show sales in the UI

[nymous]

Now that we handle paying subscriptions and buying articles, and that we generate sales and invoices for that, we should display them in the UI.

Add a new section in the "Users/show" template to list the sales, showing the date, price, and allowing the user to download the invoice.
Make sure permissions are checked: a user should only see their own sales/invoices, only have "read" rights on them. An admin can do everything.