Wasm client pings the server every second

This prevents disconnects when the server is behind Nignx.  Resolves
#35.

common/constants.go

@@ -5,6 +5,7 @@ type ClientDataType int
 const (
 	CdMessage ClientDataType = iota // a normal message from the client meant to be broadcast
 	CdUsers                         // get a list of users
+	CdPing                          // ping the server to keep the connection alive
 )
 
 type DataType int

wasm/main_wasm.go

@@ -261,6 +261,7 @@ func main() {
 
 	// This is needed so the goroutine does not end
 	for {
-		time.Sleep(time.Minute)
+		websocketSend("", common.CdPing)
+		time.Sleep(time.Second)
 	}
 }