Add Oracle and Worker to API

[keith-turner]

Inorder to easily support different methods of running Fluo (for example Mesos), it would be nice to add the Oracle to API. Maybe something like the following :

    FluoConfiguration conf = ...;
    Oracle oracle = FluoFactory.newOracle(conf);
    oracle.start();
    //wait for signal to shutdown
    oracle.stop();

Worker is too generic... thinking NotificationProcessor may be a better name to use in the API.

   FluoConfiguration conf = ...;
   NotificationProcessor ntfyProc = FluoFactory.newNotificationProcessor(conf);
   ntfyProc.start();
   //wait for signal to shutdown
   ntfyProc.stop();

Could possibly implement Guava Service