Merge pull request #188 from indikasampath2000/performance

msgId2MsgData HashMap changed to ConcurrentHashMap and getMetaDataList changed to get batch records 1000 wise
Move message scheduled to deliver increment to set before thread.
Handle message DLC move exception.
Merge pull request #189 from akalankapagoda/incrementerUpdate

Move message scheduled to deliver increment to set before thread.
Add comment to explain logic behind getMetaDataList method