qt: Move transaction notification to transaction table model

Move transaction new/update notification to TransactionTableModel.
This moves the concerns to where they're actually handled.
No need to bounce this through wallet model.

- Do wallet transaction preprocessing on signal handler side;
  avoids locking cs_main/cs_wallet on notification in GUI thread
  (except for new transactions)
Merge pull request #5168

023e63d qt: Move transaction notification to transaction table model (Wladimir J. van der Laan)