Ethereum - Implement standard wallet

**Feature description**

Ethereum standard wallets

**Is your feature request related to a problem? Please describe.**
Wallet does not support ethereum standar wallets

**Describe the solution you'd like**
Manage wallets similar to geth nodes, a wallet will be conformed by a directory filled with multiple files reprensenting a private key. Keys are stored as encrypted JSON files according to the Web3 Secret Storage specification, see https://github.com/ethereum/wiki/wiki/Web3-Secret-Storage-Definition for more information.

**Additional context**

TODO: Find a golang library for Ethereum
Requires #246

**Possible implementation**

- [ ] Create standard Ethereum wallets (backend)
- [ ] Create standard Ethereum wallets (GUI)
- [ ] List standard Ethereum wallets
- [ ] Encrypt / decrypt files for standard Ethereum wallet
- [ ] Implement `core.Wallet` interface
- [ ] Implement `core.Signer` interface

Start by reviewing the dependency on issue #246, the existing core.Wallet and core.Signer interfaces, and the Web3 Secret Storage specification linked in the issue. Identify the Go library and repository entry points for backend and GUI wallet handling. Done means creating, listing, encrypting, and decrypting standard Ethereum wallet files while satisfying both interfaces.

Written by the indexing model from the issue text.