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.
Yes, the latter, but with the above caveat (to age-out a cache entry - it's an option on the guava-based Cache): The invalidation is done only when the schema changes or index is removed/added which also means there is no need for periodic scanning of stats table.

This will be much simpler and we only have to manage a single cache. Perf should be fine - it's just an extra Scan and if it was done recently will be in the block cache anyway.

Make sure you update the size of PTableImpl by taking into account the size of a PTableStatsImpl so the cache is sized correctly.