Implement BIP32/39/44 for seed, hierarchical deterministic wallet

[chill117]

The app uses a single private key and re-uses the same address to send payments/double-spends. This is not a current best practice. Instead, the app should follow BIP32 to generate a master private key, BIP39 to generate the mnemonic seed phrase, and BIP44 to generate addresses in a deterministic way. Change should be sent to a newly generated change address for every transaction that is created and broadcast. The receiving address should also be a newly generated, un-used address.