LUCENE-5700: Add oal.util.Accountable and make all classes that can compute their memory usage implement it.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1598479 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5701: Move core closed listeners to AtomicReader.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1598487 13f79535-47bb-0310-9956-ffa450edef68