v0.8.0: Random seed correction, sorted transactions, RBF

Notable changes since last release (v0.7.1):

• Well known keypairs have been updated (this affect users running test networks);
• An intermittent error in UTXODB will no longer be silence, instead the node will properly report it;
• Nodes will now replace transactions in their TxPool if it fulfill certain conditions (e.g. higher fee);
• Random seed calculation was wrong (involved an extra Hash.init parameter) and has been fixed;
• Transactions will now sort their inputs and outputs;
• Ledger will now do a full reset if the validator set is empty, regardless of the UTXOSet being non-empty;