The sense of the "Only show active customers" checkbox was inverted.
Finish implementing the "Show zero balance owners" filter option.
It always showed nothing before.
Change gncOwnerGetBalanceInCurrency to only cosider lots that contain an invoice.
This function is currently only used in the owner tree code and this change
will cause payments not properly linked to invoices to be ignored when computing
owner balances.
Use guint64 instead of uint64_t with G_GUINT64_FORMAT to avoid warnings.