NEXUS-5577: Bumping MI to ASF 5.1.1

This updates MI from "internal" release of MI,
and contains other changes too, like bumping Lucene
patch version to 3.6.2.
NEXUS-5577: Related: bumping lucene in timeline plugin

Not related directly to NEXUS-5577, but to keep both instances
of Lucene embedded in plugins aligned. We have two lucene's, one in
indexer and one in timeline plugin.
Merge pull request #762 from sonatype/nexus-5577-maven-indexer-bump

NEXUS-5577: Maven Indexer bump to ASF released one