Removed code for listening socket.

There will be no listening socket anymore. Entry request should be
handled by recvSocket.
No special treatment is needed for entrying to network, especially no
reply message to entrying node, so separate socket and thread is not
needed.
IncommingMessageReceiver is using events mechanism

IncommingMessageObserver is not needed anymore because
IncommingMessagesReceiver uses events mechanism instead of explicitly
implemented observer design pattern.