Statistics System

Highlight of the Commit, just for review not to be merged in current state.

* Implemented StatisticsService class which creates a EventBus class (from google guava) for managing events. (Currently this is a sync event bus for testing purpose). Should add grill.event.bus.sync to grill defaults to set it to false. 
*  Added an IStatisticsStore interface which new stores can be added, currently only LogStore is available, In future we can added DatabaseStore and so and so forth to store statistics Information.
* Added an IStatisticsFormatter interface which can be used to format a particular statistics event. Currently default implementation is a JSON Formatter.
* Added Utility class to monitor log files and create partition on the hive metastore.


There is one more getTable api to say whether to throw exception or not, when table does not exist. In that case if table does not exist, it returns null