Added an InvalidMessageTypeException - thrown whenever we encounter a MessageType that isn't recognised or isn't supported.

Added EncoderFactory. This creates specific MessageEncoders. Supports JoinAcceptance and RequestToJoin.
Added MessageEncoder interface.
Added JoinAcceptanceEncoder.
Added encode(AC35Data) function to RaceVisionByteEncoder.
Added RequestToJonEncoder.
Updated RequestToJoin and JoinAcceptance decode/encode tests to use the above.

issue #35 #36
#story[1095]

racevisionGame/src/test/java/network/MessageDecoders/RequestToJoinDecoderTest.java

@@ -1,5 +1,6 @@
 package network.MessageDecoders;
 
+import network.Exceptions.InvalidMessageException;
 import network.MessageEncoders.RaceVisionByteEncoder;
 import network.Messages.Enums.RequestToJoinEnum;
 import network.Messages.RequestToJoin;
@@ -20,10 +21,10 @@ public class RequestToJoinDecoderTest {
      * @param message Message to encode/decode.
      * @return The decoded message.
      */
-    private RequestToJoin encodeDecodeMessage(RequestToJoin message) {
+    private RequestToJoin encodeDecodeMessage(RequestToJoin message) throws InvalidMessageException {
 
         //Encode.
-        byte [] testEncodedMessage = RaceVisionByteEncoder.requestToJoin(message);
+        byte [] testEncodedMessage = RaceVisionByteEncoder.encode(message);
 
         //Decode.
         RequestToJoinDecoder testDecoder = new RequestToJoinDecoder(testEncodedMessage);