Load & Save observations externally

[tomerk]

Should be able to load bulk observations into a model from an external data source & do a retrain w/ those, and save observations to an external store

[dcrankshaw]

Expanding on this a little bit. This should not require the user to bulk load observations at startup. Instead, we will add another observations API endpoint that can add several observations for multiple users at once. This endpoint should take a local filename to load the observations from or a json object listing the observations. After all observations have been loaded, it will retrain the model for each user that got a new observation once.

[dcrankshaw]

@tomerk Have you thought at all about a good way to do this?

[dcrankshaw]

This is partially addressed by #70, but that PR only adds support for loading saved observations from an object file. We still cannot bulk load observations from an external source (like a CSV file). The recommended approach for now is to script bulk-loading on the client side and send a request per-observation.