Rw/seller sees new auction

### What's this PR do?

This PR allows for sellers to register Debtors in the system - to be approved by the admin. The concept of a debtor is a business that owes money to the company. For instance, they have agreed to purchase a set of goods, and thus an invoice has been issued to which the Debtor owes the balance (of the invoice) the company that has sold it.

In order to create an auction on IX, the Seller needs to register their debtors and wait for approval by the admin. Once approved, the debtor should see 'approved debtors' in the new auction page.

### Where should the reviewer start?

The `app/views/auctions/new` is the starting place for this feature. It shows approved and pending debtors. If there are no approved debtors, the seller can register a new debtor. This begins the process of creating the debtor with a default status of 'pending'.

As you'll see, the Admin can approve the Debtor in ActiveAdmin, after which the Seller will see their debtor as approved.

### Any background context?

The Debtors are essentially a reference for the admin to determine whether the invoice (directly associated with the debtor) is worthy of posting on IX for auction. As a result, the Debtor model has a lot of informational attributes - which I'm probably going to keep in one table, since the Seller will likely always have to fill out all fields to create a debtor.