Phoenix 180

First revision for review.  There are some open points here.  Still no test case added to consume the stats.  Will do the performance test once the system is available with me.
StatisticsScanner is something we may need if we want to collect the stats as part of major compaction.
StatisticsWriter may be can be simplified and merged. similarly with StatisticsValue, can be made an inner class (POJO like class)
StatisticsTracker i think it would be needed so that we could extend that and impl that in the observers.
StatisticsUtils are just util methods to add some utitilites to extract the table name, region name from the STAT table's row key.
StatisticsTable is a wrapper on the STATS HTable.