Correctly categorize refunds and reimbursements

We need the ability to assign refunds or reimbursements back to the original expense category.

For example, if you book a hotel, then cancel and get a refund, the incoming transaction should be categorized as Travel and not as Income.

Another example: you eat out with a friend, pay for both of you, and your friend then sends you their share via Venmo. We need to categorize this Venmo transaction as Eating out, even though it is an income transaction.