OAK-593: Segment-based MK

Inline the list of identifiers of referenced segments into the
segment byte sequence. This avoids the need to keep the identifiers
in memory when they're not being accessed.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1535774 13f79535-47bb-0310-9956-ffa450edef68