FEATURE REQUEST: Export encrypted Ethereurm keystore wallet json text & file

In an Ethereum ecosystem-centric release of Gordian Seed Tool, it should export what is known an Ethereum wallet "keystore" file, which is a single derived hd-key for a single account (typically m/44'/60'/0'/0 for the first Ethereum wallet account), that is encrypted on disk and save as JSON text saved with a `.UTC` filetype.

Though Ethereum wallet keystores are not well supported in their creation (mostly generated by the Ethereum Geth Client, and the MEW (MyEthereumWallet.com) wallet), they are reasonably well supported for import (Metamask and many more).

We want to support Keystores as they help enforce key separation. Most ETH wallets want the full seed so that they can generate all accounts for all coins, but that isn't as safe as only providing a single derivation (for instance, an account only for holding ERC-721 NFTs). This key separation isn't ideal, but a start that works with existing wallets in the ETH ecosystem.

As a reference, our "ffa11a8 - 604b93f2 - 128-bit Seed Public Test Vector (Yinmn Blue)", in BIP39 words is:
```
fly mule excess resource treat plunge nose soda reflect adult ramp planet
```
…and saving the keystore with the password "password", the default files generated by the MyEtherWallet.com & MEW Chrome Extension are:

[Reference Yinmn Blue Keystore UTC Files.zip](https://github.com/BlockchainCommons/GordianSeedTool-iOS/files/8120360/Reference.Yinmn.Blue.Keystore.UTC.Files.zip)

and the JSON inside is:

```json
{"version":3,"id":"bd9e9721-a550-4684-a327-e113a3676aae","address":"557525d043656e9385d8efaa9cd4a3aeade01168","crypto":{"ciphertext":"dffd2024ca1fdf78616fd1a9f55d09e2ba990e142c3b25d62b5305b19ba0e42e","cipherparams":{"iv":"d29d67b60926cdb55402d798474d2210"},"cipher":"aes-128-ctr","kdf":"scrypt","kdfparams":{"dklen":32,"salt":"c1252943cbed044097fcfbb0796bb422f571eb6512d780291a22c92379851fed","n":131072,"r":8,"p":1},"mac":"d7494f0d3c039f29a762b929ea087377114ef1889acdc6460b19e7c6d08ffb25"}}
```

Or prettified:
```json
{
"version": 3,
"id": "bd9e9721-a550-4684-a327-e113a3676aae",
"address": "557525d043656e9385d8efaa9cd4a3aeade01168",
"crypto": {
"ciphertext": "dffd2024ca1fdf78616fd1a9f55d09e2ba990e142c3b25d62b5305b19ba0e42e",
"cipherparams": {
"iv": "d29d67b60926cdb55402d798474d2210"
},
"cipher": "aes-128-ctr",
"kdf": "scrypt",
"kdfparams": {
"dklen": 32,
"salt": "c1252943cbed044097fcfbb0796bb422f571eb6512d780291a22c92379851fed",
"n": 131072,
"r": 8,
"p": 1
},
"mac": "d7494f0d3c039f29a762b929ea087377114ef1889acdc6460b19e7c6d08ffb25"
}
}
```

Here are some links about keystores:

* https://cryptodefinitions.com/myetherwallet-guide-part-1-using-the-keystore-file/
* https://julien-maffre.medium.com/what-is-an-ethereum-keystore-file-86c8c5917b97
* https://cryptobook.nakov.com/symmetric-key-ciphers/ethereum-wallet-encryption
* https://help.myetherwallet.com/en/articles/5449827-what-is-a-keystore-json-file-can-i-change-my-password
* https://eips.ethereum.org/EIPS/eip-601

For reference, here are the first 5 ETH account paths for Yimn Blue:

```
#0
0x557525d043656e9385D8EFAA9Cd4a3aeAdE01168

#1
0xc11922071b93B306866e79914C7cdA610b896D26

#2
0x642A049CD438e1B3Cffd4462128CD4ca3d91c00a

#3
0x1C46E9ceeDF0699887286E1D0cFC60B9146233A3

#4
0xa24b1107350FE2F2051b1fF0071A0BDBcb34cBcf
```

Here are the derivation paths that MyEtherWallet supports (we should only support the top 5 or 10 or 20 top market cap or transaction cap ones)

```
[m/44'/60'/0'/0 - Ethereum]()
[m/44'/61'/0'/0 - Ethereum Classic]()
[m/44'/1'/0'/0 - Ropsten Testnet]()
[m/44'/60'/0' - Ledger]()
[m/0'/0'/0' - SingularDTV]()
[m/44'/40'/0'/0 - Expanse]()
[m/44'/108'/0'/0 - Ubiq]()
[m/44'/163'/0'/0 - Ellaism]()
[m/44'/1987'/0'/0 - EtherGem]()
[m/44'/820'/0'/0 - Callisto]()
[m/44'/1128'/0'/0 - Ethereum Social]()
[m/44'/184'/0'/0 - Musicoin]()
[m/44'/6060'/0'/0 - GoChain]()
[m/44'/2018'/0'/0 - EOS Classic]()
[m/44'/200625'/0'/0 - Akroma]()
[m/44'/31102'/0'/0 - EtherSocial Network]()
[m/44'/164'/0'/0 - PIRL]()
[m/44'/1313114'/0'/0 - Ether-1]()
[m/44'/1620'/0'/0 - Atheios]()
[m/44'/889'/0'/0 - TomoChain]()
[m/44'/76'/0'/0 - Mix Blockchain]()
[m/44'/1171337'/0'/0 - Iolite]()
[m/44'/137'/0'/0 - RSK Mainnet]()
[m/44'/37310'/0'/0 - RSK Testnet]()
[m/44'/1001'/0'/0 - ThunderCore]()
[m/44'/997'/0'/0 - Solidum]()
[m/44'/916'/0'/0 - Metadium]()
[m/44'/237'/0'/0 - DEXON Network]()
[m/44'/60'/0' - Lightstreams Network]()
[m/44'/227'/0'/0 - MintMe.com Coin]()
[m/44'/466'/0'/0 - EtherCore]()
[m/44'/60' - Avax C-chain]()
```

Start with the supplied Yinmn Blue seed vector, reference UTC archive, JSON example, and listed derivation paths. Done means producing an encrypted single-account keystore export that matches the requested Ethereum-compatible JSON structure and supports the selected path and password.

Written by the indexing model from the issue text.