Store history of evolved samples in map-elites.

[herbiebradley]

    https://github.com/CarperAI/ELM/blob/6bf347c13301afadfb093616a6b84d64a59a686f/map_elites/map_elites.py#L59-L62

To support replicating the datasets for Stage 2, we'll need to record all examples mapped to the archive without discarding them.

Not sure if this is within scope of the stage 1 commit, but what's a good way to add support for this option (for ELM sodaracer), while keeping this more general as a map_elites implementation? Would this make sense as a parameter/option in the env that can be checked?

Originally posted by @daia99 in #9 (comment)