Add support for default "transfer" account in double entry mode

I am creating this pull request against your develop branch, but since I developed the code against main, I have not tested against your develop branch. 

If I will develop against your "develop" branch, but that would mean that I am working with something unstable.

I don't know how to resolve this since I don't want to be testing unstable code while working on a feature myself.

But, for now, here is the pull request.