Provide an initial implementation

Created by: rjw57

This series of commits takes the upstream unattended install scripts into those we can use for installing a lecture capture agent.

See each commit for a discussion of what has been changed.

At the end, we introduce some CircleCI configuration which will automatically build the image and upload it to https://uisautomation.github.io/lecture-capture-agent-bootstrap for easy access.

Update: an example of the auto-deployed documentation is at https://rjw57.github.io/lecture-capture-agent-bootstrap/.