Convert GnuCash account type to valid top-level account type

The GnuCash template may use any account type for top-level account
groups. KMyMoney only supports certain types. The current conversion did
not take that into account and some templates failed during loading into
KMyMoney.

This change adjusts the account type of the top-level accounts to those
supported by KMyMoney and makes the templates loadable.

CCBUG: 452863