Adds TransactionDataset.GetValue(bool, string accountId), which
negates the value when the given account is the transaction's origin
(paying out) so the account's own transaction list and charts show
a minus sign for outgoing money, regardless of account class. Removes
the old Activa-only sign flip baked into
ViewService.GetTransactionViewListAsync(accountId), which would have
double-negated Activa bookings against the new accountId-aware
GetValue. ChartService's booking-text totals now sum through the same
accountId-aware GetValue instead of filtering to inbound transactions
only, so a booking text nets its in/out transactions correctly.
