Use earliest of block and receive time for tx timestamp.
Use earliest of block and receive time for tx timestamp.

This corrects an issue where seed-restored wallets report the time of
restore as the transaction time and fixes timestamps for transactions
received when the wallet was not running or connected to the network.

decred/dcrwallet,jrick/btcwallet,decred/dcrwallet,jrick/dcrwallet,jrick/dcrwallet,jrick/btcwallet