[ADD] add constant identifiers to JSONConvert and made serverclient and client use them

SharedClientServer/JSONConvert.cs

@@ -7,6 +7,10 @@ namespace SharedClientServer
 {
     class JSONConvert
     {
+        public const byte LOGIN = 0x01;
+        public const byte MESSAGE = 0x02;
+        public const byte LOBBY = 0x03;
+        public const byte CANVAS = 0x04;
         public static (string,string) GetUsernameAndMessage(byte[] json)
         {
             string msg = Encoding.ASCII.GetString(json);
@@ -21,6 +25,11 @@ namespace SharedClientServer
             return payload.username;
         }
 
+        public static byte[] GetUsernameMessage(string username)
+        {
+
+        }
+
         /// <summary>
         /// constructs a message that can be sent to the clients or server
         /// </summary>