GX-654 - Added Snappy as a dependency.  Added compression layer.
GX-654 - Added another constructor to DatagramEventListener which takes
an enqueuer and dequeuer as arguments.  The default constructor calls
this with new instances of DatagramEnqueuer and DatagramDequeuer. 
Created a SnappyDatagramEventListener which uses this new constructor to
use a SnappyDatagramDequeuer.