Command Line Wallet Backend
I think it would be cool if we had a backend that uses the `monero-wallet-cli` command to interact with a wallet. The backend could take a path/alias/command to the `monero-wallet-cli` executable and a path to a wallet file. Then we would be able to write something like this:

    from monero.wallet import Wallet
    from monero.backends.cli.wallet import CLIWallet

    wallet = Wallet(CLIWallet(wallet_path='~/Documents/mywallet', exe='/usr/local/bin/monero-wallet-cli'))

    # normal wallet commands

I could start working on it if you think its a good idea. The advantage of this is that you don't have to have a wallet server running on your computer.