Moved DeployMessage's into its own DeployMessages object.
Also renamed MasterState to MasterStateResponse and WorkerState to WorkerStateResponse for clarity.
Removed Cache and SoftReferenceCache since they are no longer used.
Moved block manager messages into BlockManagerMessages object.
Moved all StandaloneClusterMessage's into StandaloneClusterMessages object.
Merge pull request #746 from rxin/cleanup

Internal cleanup