GIRAPH-704: Specialized message stores (majakabiljo)
GIRAPH-705: Type converters and giraph-hive cleanup (nitay)
GIRAPH-710: Define zookeeper version in a property to allow build time override (apurtell via nitay)
GIRAPH-708: Factories for creation of all IVEM types (nitay)
GIRAPH-709: More flexible Jython script loading (nitay)