Saved Keypairs: add fund with Friendbot

[quietbits]

This feature will be helpful after the network resets.

• Fund with Friendbot button if an account is not active
• Show XLM balance if an account is active

Design

[janewang]

Warning Message on top: Saved keypairs are stored in the browser's localstorage unencrypted and with no protection. Anyone using this browser will be able to access the keys and the keys could be easily lost. Do not save keys that are intended to hold or control value on mainnet. Do not reuse keypairs from futurenet or testnet on mainnet for security. For keys that will hold value, please consider using a Stellar wallet.