Issues #15, #16 as well as new public service to get at some cluster info

taskExecuted timer fixed.  Logging is now based on Slf4J using the
lombok extension @Slf4j.  Added ClusterService devs can get at via
HazeltaskInstance which will give access to some useful data on how
much work is in the system, where it is, and the option to clear group
queues.
quick fix for NPE in test
Lite members should be included
Cancel task, Clear group, Simplified DistributedFuture