decouple gearman from the gearman configuration

This change is to create a new object to store Gearman
objects and state info.

src/main/java/hudson/plugins/gearman/GearmanProxy.java
  created to keep Gearman state info.

src/main/java/hudson/plugins/gearman/GearmanPluginConfig.java
  simplied this class by removing the core gearman stuff out to
  a GearmanProxy.java class

src/main/java/hudson/plugins/gearman/Constants.java
  Use one logger instead of two.  updated logger reference in all
  of the other files in this checkin

src/main/java/hudson/plugins/gearman/ProjectListener.java
src/main/java/hudson/plugins/gearman/StartJobWorker.java
src/main/java/hudson/plugins/gearman/StopJobWorker.java
src/main/java/hudson/plugins/gearman/ComputerListenerImpl.java
  update references to changed class and methods

Change-Id: I879cdb8839c8b5437bccf6d7e1602c33eff434a6