Add configuration options to bnbcli

[karzak]

When using bnbcli, the user must always specify the --node and --chain-id flags. To make commands less verbose, add a config command that is saved to $HOME/.bnbcli/config/config.toml

bnbcli config node "tcp://dataseed1.binance.org:80"
bnbcli config chain-id "Binance-Chain-Tigris"

If the --node and --chain-id flags are not specified, bnbcli should check the config file and use those values if they exist.