Allow users to mark transactions as "payments" or "transfers", which are excluded from income and expense calculations

[zachgoll]

Overview

Our current UI displays several "income" and "expense" metrics for transactions, and allows a user to "exclude" a transaction from these calculations.

While this is an acceptable UI, we should treat "Transfers" (generic) and "Debt Payments" (a specific type of transfer) as first-class citizens in the app as they apply to nearly all users globally.

Requirements

• User can mark transactions as "transfers" through bulk editing
• User can add a transfer
• User can specify whether a transfer is "generic" (i.e. "cash") or a specific type of transfer (i.e. "credit card payment" or "brokerage withdrawal")
• All transfers and subtypes should be excluded from income/expense calculations
• (future requirement) this setup should support "linking" transfers as described in this project item