add new class to hold common constants; update message types
Continue integrating listener. Many inconsistency...
listerner terminal can receive unicast msg. Update variable names to be more meaningful

TODO: figure out source of msg at receiption
Update sendMsg sigature to include real content, if any

TODO: 0) Listener parse new formatted rcv msg: esp type and source -
Han contact Dan when get this done to try 1)
1) try multicast - Dan
2) guesser start timer at rcv - Han
3) actor update answer boards etc at rcv - Han