Fix useGroupingFromString method name
Extract real consistent hash from GroupingConsistentHash
LocalityHints throws IllegalStateException if a string with no locality hints is provided
Fix FenixFrameworkGrouper

* Removed the dependency to FenixFramework since it originates a deadlock when
accessed during the FenixFramework initialization.
Add membership listener to remove leavers
Removed lower bound configuration for B+Tree

* Now, it is only possible to configure it via JVM property by setting
-DbtreeLowerBound=XXX