Add the store RPC

[azalty]

https://www.getmonero.org/resources/developer-guides/wallet-rpc.html#store

Could you please add the store RPC? It asks monero-wallet-rpc to save the wallet file, if it created subaddresses for example so they aren't lost. See monero-project/monero#4673

[lalanza808]

you could always just use monero.backends.json_rpc.wallet.raw_request

I made PR #133 though