Scalding type safe API support

The Scalding Fields API is deprecated and [recommended to be avoided](https://github.com/twitter/scalding/wiki/Type-safe-api-reference#interoperating-between-fields-api-and-type-safe-api). 

It would be nice to make `HBaseSource` work with the [Type Safe API](https://github.com/twitter/scalding/wiki/Type-safe-api-reference) as a source and sink.
