The typeahead functionality on the register's account should be consistent across the application. It doesn't work on the Bill Expense Account / Invoice Income Account fields 

Reproduce:
- Introduce the account code on the bill expense account and type TAB or enter

What happens:
- Gnucash says the account could not be found and asks me if I want to create it

What should happen:
- Gnucash search for the account code and replaces the account code for the real account name on the input field.

More info: https://lists.gnucash.org/logs/2018/04/10.html#T17:34:07