Merchant Items Index: 5 most popular items

[avjohnston]

As a merchant
When I visit my items index page
Then I see the names of the top 5 most popular items ranked by total revenue generated
And I see that each item name links to my merchant item show page for that item
And I see the total revenue generated next to each item name

Notes on Revenue Calculation:

• Only invoices with at least one successful transaction should count towards revenue
• Revenue for an invoice should be calculated as the sum of the revenue of all invoice items
• Revenue for an invoice item should be calculated as the invoice item unit price multiplied by the quantity (do not use the item unit price)