The HBaseDatasetRepository now supports loading a dataset that is
a composite of multiple HBase datasets that share a table. Prior
to this, one had to create a dataset of the composite, but with
this change, creating a composite is now loaded at runtime (only
the sub entities need to be created).

The one downside to this is that the Dataset created now returns
a Map type instead of an entity that has member fields that make
up the composite type.