Unified data mode handling for output objects

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Issue #287 adds data mode selection (by visit / by home) for pipeline simulations, which is similar in spirit to the dual output capturing of BasicSimulator. Two thoughts arise from this:

1. It would be nice to unify the data mode handling between all of our systems. Should we retrofit BasicSimulator to follow the pipeline simulations method?
2. Even so there may be cases where users want both modes (or multiple modes, generally). Can we make it so users can opt into multiple modes and just get multiple output objects as a result?