Remove specific dimension / fact load stage definition.
Fix truncate_pre_load on stages.
Any generic sink can be truncated pre-load.
Pull full_reload up to StageBuilder.

Change how default sinks/transformations get created.
Remove DatasetBatchStage.

Stages are now generic, can be configured via injected procs rather
than relying on inheritence.
Remove some differences/shared code from SchemaTableStageBuilder.

Goal is to remove this class completely, and deal with differences by
whatever composed objects are in use.
Stages can be marked as executable or not.
Version bump to 0.2.2