aqbanking6: Added compatibility functions for KMyMoney.
KMyMoney uses AB_Banking_GetAccountByAlias() in AqBanking5, which in
turn uses application-specific data storage provided by previous versions
of AqBanking. I planned to removed that in AqBanking6. However, to port
the kbanking plugin faster to AqBanking6 these fucntions have been put