A series of performance optimizations to support importing larger datasets

-  Set RevTreeBuilder default normalization threshold to 1M, and default max heap to 2GB.
-  Refactoring internal to org.geogit.api.Node to use less memory
-  Cache only bucket trees
-  New ObjectId.createNoClone(byte[]):ObjectId factory method
-  WorkingTree.insert(Iterator<Feature>, ...) calls in ObjectDatabase.putAll 
-  RevFeature and RevFeatureType maintain the original FeatureType attribute order
-  Use an intermediate byte buffer in JEObjectDatabase.putAll()

Additionally, the BDB JE object database create a default je.properties configuration file. In the future we could indicate somehow when an operation works on bulk data so that the database can be opened in "bulk mode".