HSEARCH-1191 : Migration to Apache Lucene 4.6

 - https://hibernate.atlassian.net/browse/HSEARCH-1191

It seems to be all working, but I have some doubts about the quality of our Serialization implementations.

Tests are all passing fine, so this might be good enough but I'd like to reiterate on this as a next step and make more complete tests (and likely fixes) for at least the Avro serialization.

This is meant to have _zero_ impact on our API, but of course users will have a fair share of pain by migrating their direct usage of Lucene APIs or custom extensions like Filters ,Collectors, creation of Queries and configuration of Analyzers.
If you see actual API changes - I might have forgotten some ? - please track them down for our migration guide.