ADD: Message container and Join Message

include/WHISPER/Messages/Protos/message.proto

@@ -0,0 +1,19 @@
+syntax = "proto3";
+
+
+import "google/protobuf/any.proto";
+
+package messages.header;
+
+// [START messages]
+message Message {
+  int32 topic = 1;
+  int32 msgType = 2;
+  int32 sourceType = 3; 
+  int32 sourceID = 4;  
+
+  repeated google.protobuf.Any payload = 5; 
+
+}
+
+