First iteration of Fire-and-Forget style UDP IO

*DO NOT MERGE YET!*

Preview of simple UDP IO based on DatagramChannel send/receive operations.

*Common code fragments were NOT extracted from TCP!* This code is based on copy-paste to have a general idea what are the common functionalities shared by various transports. 

Two modes are supported:
 - Bind-and-send where sender port is set to the listen port
 - Simple-send, where no answer is expected and no listen port allocated