Add genwallet.py script

[nixbitcoin]

This PR adds my version of @AdamISZ's genwallet.py from #683.

I'm not very familiar with the intricacies of JoinMarket's testing infrastructure, so maybe somebody else could add a simple test for this script.

Closes #683

[AdamISZ]

Nice, thanks. I guess it makes sense to add an option for wallet type; in particular considering #656 and some other use cases for bech32 already (e.g. payjoin).

[AdamISZ]

In 2f53c5f I added (admittedly fairly trivial) tests to check that when a wallet file is created with create_wallet, it can be opened with the specified password, and has matching secrets. Feel free to edit if you like.

[kristapsk]

This duplicates functionality of wallet-tool.py generate, I'm wondering can't we figure out a way to just do a non-interactive way to do it using wallet-tool instead of having two scripts.

[AdamISZ]

This duplicates functionality of wallet-tool.py generate, I'm wondering can't we figure out a way to just do a non-interactive way to do it using wallet-tool instead of having two scripts.

Very fair point yeah. This same code could be trivially repurposed as just another method in wallet-tool (if anyone is so inclined they could open another PR with that alternative). Another angle might be: make a subdirectory under scripts/ for "advanced/developer tool" scripts.

Personally I'm quite focused on moving in the direction in #670 (an RPC API), so I'm a bit less interested in exactly how to add more functionality into the scripts.

[AdamISZ]

I feel like it's fine to just add this script as-is, even if there's an argument for folding it into the wallet-tool script (it could always be done later). Ordinary users won't need this anyway. Agreed @kristapsk ?

[kristapsk]

@AdamISZ Agree

[kristapsk]

ACK 2f53c5f