UTXO Watchlist

[pkahly]

• Add a flag for adding utxo to watchlist
• Unspent mining rewards will be added automatically during install (but not after that)
• Each watch item will be checked against the utxo set each iteration and alerts will be sent if they are not found

[pkahly]

Convert find_old_utxo.py into a function that can be run via a main.py flag.

Add parameter for block height threshold

[pkahly]

Only remaining work is to check the watchlist against the utxo set.

This will probably take a while, so it may only be practical to do once per day, etc