cmd/lncli: add closeallchannels command

In this commit, we add a new closeallchannels command to lncli. This
command allows us to close all existing active and inactive channels
by closing them cooperatively or unilaterally, respectively.

cmd/lncli/main.go

@@ -170,6 +170,7 @@ func main() {
 		disconnectCommand,
 		openChannelCommand,
 		closeChannelCommand,
+		closeAllChannelsCommand,
 		listPeersCommand,
 		walletBalanceCommand,
 		channelBalanceCommand,