From version 1.12.5, the “Import Data” menu has been removed. The functionality is still available, though.
For bulk creation of Invoices, just go the the admin page to add a new Invoice. Instead of creating a single Invoice for one specific Member, you can select a Member Category and create a batch of new Invoices by following the steps in the wizard at the bottom of the page.
Similarly, import Members from a CSV file by using the admin page to add a new Member. At the bottom of the page, a CSV file can be entered to upload an existing member list to your site.