DERBY-6733: Implement an MBean for monitoring caches

Add a new MBean called CacheManagerMBean, which provides information
about a CacheManager instance.

Create CacheManagerMBean instances for the page cache and the
container cache when a database is booted.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1624469 13f79535-47bb-0310-9956-ffa450edef68