Allow more family/tablet customization

[greglook]

Currently tables allow for customizing how records are stored in each partition by assigning them to tablets via families. This should be generalized so that other per-family settings can be customized, such as the data format that the family's tablet is stored in. This could allow for more efficient or customized formats for different kinds of data - using ORC or Parquet for high-performance storage, or EDN/CBOR for flexibility, etc.