Update identity partition builder methods, cardinality

Identity partitioners should all use Object as their source and partition type, so there is no longer a need to require it in the builder API. We can leave it in the partition expression for now because it's working and we need to transition to partition config files in the new format.

With HBase partitioning unified with core, the cardinality required for some partition functions is less useful. We should default the cardinality in most places, except for the hash partitioner. There has also been an open pull request (#10) for a while.