Print version string at startup.
Print version string at startup.

This makes btcwallet match btcd's behavior.

Initially pointed out in:
decred/dcrwallet#125

btcsuite/btcwallet,synrg-labs/btcwallet,Roasbeef/btcwallet,Stash-Crypto/btcwallet,btcsuite/btcwallet,decred/dcrwallet,jrick/btcwallet,jrick/btcwallet,jrick/dcrwallet,Roasbeef/btcwallet,synrg-labs/btcwallet,decred/dcrwallet,jrick/dcrwallet,Stash-Crypto/btcwallet