Memory and GC stats for management center

Ported from elastic-hazelcast

-Moved GCStatsSupport, MemoryAllocator, MemoryManager, MemoryStatsSupport to hazelcast from hazelcast-enterprise
-I've renamed GCStats/MemoryStats to LocalGCStats/LocalMemoryStats and also moved them to com.hazelcast.monitor package.
-Added "getMemoryManager" method to SerializationService interface (to be implemented on the hazelcast-enterprise side)