Create a way to save sessions in the QA pipeline

## Objective
Support progress toward the [Deploy REST API...][1] by _implementing conversation sessions_

## Key Result
- [ ] Commit code for **generating** a `session_token` and including that `session_token` in the response body of each request (see the `requests` package in Python)
* @foaad suggested that sessions should expire.
- [ ] Commit code to capture the metadata for each pass through the QA pipeline (store: question, answer, timestamp, ...)
- [ ] Commit code to store sessions in the database
- [ ] Commit code to continue off of an old session by providing the old `session_token`
- [ ] Publish documentation for how to use the `session_token`

## Details

**Additional context**
* Don't reinvent the wheel!
* https://stackoverflow.com/questions/12737740/python-requests-and-persistent-sessions

[1]: https://github.com/calpoly-csai/api/milestones