Detect if a transaction from the mempool is missing dependencies and skip it

[andreabadesso]

After https://github.com/HathorNetwork/hathor-wallet-service/issues/242 is done, we will receive a specific error message if a transaction is missing dependencies

If this transaction was sent during the mempool sync, we are safe to ignore the error, as the transaction will be sent again during the block sync (after it is confirmed by a block) or during the next mempool sync (if it is still on the mempool)

If this transaction was sent during the block sync, we should alert and stop the sync as it indicates that something is wrong and the wallet-service database is corrupted somehow.

This should avoid false positives alerts for our on-call