Reply to outbox messages
show next transaction time when sending message

 * add nextTransactionTime variable to the client to store the next transaction absolute time
 * show when next transaction will happen in the "Created new outbox..." message
 * remove second decimals from "Next network transaction..." log message
Merge branch 'duy/nexttransactiontime' into merged

Conflicts:
	client/client.go
Merge remote-tracking branch 'duy/replyoutbox' into merged