ISPN-4966 The <backups/> element should be a sub-element of all cache-types, not just clustered caches
Update locking documentation

* added how it works in clustered caches
ISPN-4970 AvailabilityException and AvailabilityMode are in the wrong package
ISPN-4970 AvailabilityException and AvailabilityMode are in the wrong package

Move the impl package as well
ISPN-4981 Update to Hibernate Search 5.0.0.Beta2
ISPN-4981 Spatial Query updated API: onCoordinates -> onField
ISPN-4902 Unsupported Class Version Error when running testsuite with JDK6

Update documentation.
Clean up generics a bit
ISPN-4951 Entry Retriever iterator should rethrow caused exception

* Pass along any local throwable to iterator
* If remote node receives throwable propagate that as a response
ISPN-4982 EntryRetriever doesn't filter and convert activated values
properly