OAK-1337: Implement RepositoryStatistics from Jackrabbit API
OAK-1338: Implement QueryStat from Jackrabbit API
Implement QueryStats and introduce StatisticManager class as central point for managing repository wide statistics.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1565271 13f79535-47bb-0310-9956-ffa450edef68