The above commit introduces auto freezing for utxos below
a threshold, but erroneously auto freezes new utxos in
almost all cases because transactions are processed
multiple times (add_utxos handles this in the wallet).
The problem here is solved as with the same issue of
duplication in the logging of new transactions; we keep
track of new txids that arrive in the wallet and make
sure not to process the same txid twice.
Additionally, the setting of WalletService.used_addresses
is fixed. Test for this function is also fixed.