Rename destination_account to payee

[sauloperez]

All the naming around transfers and movements is rather cumbersome and not immediately obvious. I suggest we rename the concept destination_account to payee. It seems to be a more appropriate term in this banking/payment domain.

This stems from #264 (comment), but it'll definitely require some investigation to understand how hard it would be.

I hope this will improve the readability of code involved with it.