[GNC] Combine user accounts

[flywire]

I posted a piecash example I wrote to create a book from csv:
https://lists.gnucash.org/pipermail/gnucash-user/2021-July/097124.html

One of the good things about piecash is it's scripted so you get the same
result every time without any wayward keystrokes, It only takes a few
minutes to install and run the fully functional example but it's not coded
to work with multisplits, and GnuCash csv export format is completely
different to import.

If the csv import example is of interest I'll tweak it to support qif if
you want it.