Support one-to-many output from select() and update(); implement ObjectProcessorSelectColumn

[rcaudy]

We'd like to be able to allow a single SelectColumn to produce multiple outputs. This is a step towards tuple-UDF support, but also will enable ObjectProcessor to be used as the backing system for a SelectColumn, possibly with some refactorings.

1. Refactor SelectColumn to refactor member functions describing the output (name, type, etc) to a List<ColumnDefinition>
2. Refactor SelectColumn to support List<ChunkSource> instead of ColumnSource for getDataView() and probably getLazyView().
3. Make any necessary changes in QueryTable or SelectOrUpdateListener to accommodate same.
4. Refactor SelectColumnLayer to be aware of multi-output SelectColumns and retrieve them together. Will probably need to use SharedContext to allow the ChunkSources to share their input/calculations.
5. Implement ObjectProcessorSelectColumn as an initial use case.