Implement a visualization tool for MATT contract executions

[bigspider]

The ContractManager keeps track of all the transactions related to the UTXOs that is tracking, including the ones that are already spent.

It would be great to have some tools to visualize the transaction graph, possibly interactive so that for each UTXO one can also inspect the info about the transaction it was contained in, the contract, the data, etc.

It could be done in two separate steps:

• The ContractManager could have a snapshot function that dumps all info about transactions, utxos, contracts, etc. into a json file.
• Optionally, the ContractManager could have an event system so that interactive visualizations could be updated in real time.
• One or more visualization tools can use a snapshot file to produce the visualizations.

It could also be integrated inside the cli examples.