Add runnable index upgrader [LUCENE-5956]

As a spinoff from discussion in #7002, I'd like to add a new module "lucene-upgrader", move `IndexUpgrader` to this, and add embed older versions of lucene (just enough to upgrade indexes) in the built version of the module's jar. This would be runnable from the command line with something like:
`java -jar lucene-upgrader-4.11.0.jar /path/to/index`

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Migrated from [LUCENE-5956](https://issues.apache.org/jira/browse/LUCENE-5956) by Ryan Ernst (@rjernst), updated Jul 10 2015

Start by reading the discussion in issue #7002 and locating the existing IndexUpgrader. Determine how a new lucene-upgrader module could package the older Lucene versions needed for index upgrades and expose the requested command-line invocation. Done means a built lucene-upgrader-4.11.0.jar can upgrade an index passed as its path.

Written by the indexing model from the issue text.