Add show_node_id to basecoind

[adrianbrink]

Generally we should export all commands from Tendermint to Basecoind.

[cwgoes]

Other Tendermint commands not yet exposed by basecoind:

gen_validator - Generate validator keypair (superseded by basecoind init?)
lite - Run lite client proxy server
node - Run Tendermint node (superseded by basecoind start?)
probe_upnp - Test UPnP functionality
replay - Replay messages from WAL
replay_console - Replay messages from WAL in a console
show_validator - Show node validator info
testnet - Initialize files for a Tendermint testnet

@adrianbrink Should all of these (less gen_validator and node) be added?

[cwgoes]

After discussion, decided we only need show_validator for now.