Logging service that writes into S3

[mtnygard]

The current log service writes to local files, which are loaded into Datomic at the end of the simulation run. This is one of the things that requires every simulation runner to be a Datomic peer.

It would be helpful to allow a substitute log service that writes through to S3. This requires the following changes:

1. Create the service and attach it to the sim.
2. Assign S3 object IDs to each runner at sim startup time.
3. Construct the service at sim-execution time. It must inject a function that accepts a data structure and serializes it to the S3 file for that runner.
4. Load S3 EDN files into Datomic at sim completion.

The recording function must be a drop-in replacement for the current recorder. It must be possible to switch this out without changing the action functions.