Add a PIR sensor to shut off display when nobody is nearby

[ke4roh]

Passive infrared can indicate when someone is present, and it can turn off the monitor to save power when people are absent.

This must be set up to work as an option. That is, if there is no PIR sensor, then the system should behave as if it were always detecting motion, or it should have an option to enable/disable PIR functionality. Ideally, it is always enabled, and if the sensor is available, it works.

Acceptance criteria:

• Instructions identify a specific PIR assembly and describe how to connect it to the Pi.
• Script(s) interpret the PIR sensor data
• The script(s) are installed on the Pi by Ansible
• The system can run correctly without a PIR sensor (by default)
• Script(s) turn off the monitor after a configurable timeout, default 20 minutes, of no PIR activity. (It would be acceptable to have this timeout default to zero to indicate no PIR sensor, and a non-zero value to also specify to use the PIR sensor.)
• Script(s) turn on the monitor immediately when there is PIR activity.