Allow for exporting/importing of accounts through Private Keys and Multiple Seed phrases in a single wallet

Currently there is no way for the users to export and import accounts for wallet with a private key.

It is not as simple and would require some changes to how we do things with the seed AFAIK we should change and use the seed from bip39 for only secret key generation.

We currently use `client.newWallet` for creating a new account but this uses seed for both secret key generation and account seed thus exporting an account would require either the full seed or secret key + account id to import the account.

As for Multiple seed phrase it is open for discussion, some wallets do it some don't.