Remove seed backup from the setup process and store the seed securely by lnd for optional backup later #545
Description
This feature would require lnd the store the mnemonic seed words securely e.g. encrypted using the wallet password chosen by the user. An addition grpc api would have to be provided to retrieve the seed words from lnd by providing the wallet password. Finally, a grpc api could be exposed to securely purge the seed words from disk after successful confirmation by the user.
The main motivation behind this change is to ease onboarding of the app by considering that most users are likely to either just test the app with testnet btc or with small amounts of pocket money before depositing any substantial amount of BTC into the wallet. Once the user does fund the wallet with an amount above a certain threshold, the app could notify the user on each startup to backup his seed.