OAK-1031: SegmentMK: Fewer segment lookups

Replace the per-segment OffsetCaches with a per-store LIRS record cache.
This way we can avoid the segment lookups for the string and template
records that quite frequently cross segment boundaries.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1527390 13f79535-47bb-0310-9956-ffa450edef68