Templates or default balancing transaction

Installed from FDroid: v0.2.18

Howdy, love the app so far. Great work! Here's a use-case I was considering:

I take the subway every day in Beijing, and I want to make an entry in my ledger when I pay my fare. Current steps to make an entry:

1. Type subway into payee box (or select autocomplete)
1. Select account expenses:transportation
1. Enter amount
1. Select balancing account
1. Hit save

I was thinking it would be nice if it went more like this:

1. Type subway into payee box
1. Enter amount for pre-populated first account (expenses:transportation)
1. Tap Save

The accounts (and potentially amounts, too) would be taken from the most recent transaction with the same payee and autofilled into the form. They could be grey or something to let the user know that they are default values. This autofill behavior already works for balancing amounts entered. If the user wants to change them, the user can start typing in the field and have it work just as if the field were empty. If the user wants to delete one, the user can just swipe it away, as is currently supported.

Alternatively, there could be some sort of template based on account. For example, expenses:food might usually balance with assets:cash. I think the former idea is more robust and easier to implement, though.

Start by reviewing the transaction-entry flow and the existing balancing-amount autofill behavior described in the issue. The request needs a product decision between recent-payee defaults and account-based templates before completion can be defined.

Written by the indexing model from the issue text.