Added Service for Storing/Retrieving Broadcasts

[rickysaltzer]

Introduced BroadcastManager class to allow the user to store broadcasts made using Spark for later use.

BroadcastManager<ComplexRecord> recordManager = new BroadcastManager<>();
Broadcast<ComplexRecord> complexRecordBroadcast = sparkContext.broadcast(complexRecord);
recordManager.put("abc", complexRecordBroadcast);