Implement Countermeasure for TX Malleability

[goergch]

TX Malleability can lead to sitauations where Txs stay in pending state forever. Detect this and react.
Track the state of transactions and allow a maximum count of pending transactions.

[goergch]

Track the pending transactions per user. If the total amount of bitcoin in this tx is greater than a limit, we deny any new orders.

[goergch]

additionaly we can send machines a list of pending tx and orders

[goergch]

additionally we can implement a timeout for a warning on invoice basis if they stay pending

[bockha]

I would love to see the credit one marketplace customer has being tracked instead of just taking the number of pending or dead transactions into account.