* [NOD-201] Implemented the AddSubnetwork CLI tool.
* [NOD-201] Fixed various bugs in AddSubnetwork.
* [NOD-201] Fixed mempool maybeAcceptTransaction verifying gasLimit for a subnetwork registry transaction.
* [NOD-201] Fixed serialization/deserialization bugs in addrIndex.
* [NOD-201] Fixed BlockConfirmationsByHash not handling the zeroHash.
* [NOD-201] Used btclog instead of go log.
* [NOD-201] Made gasLimit a command-line flag. Made waitForSubnetworkToBecomeAccepted only return an error.
* [NOD-201] Filtered out mempool transactions.
* [NOD-201] Fixed embarrassing typos.
* [NOD-201] Added subnetwork registry tx fee + appropriate cli flag.
* [NOD-201] Skipped TXOs that can't pay for registration.
