Monitor a single file on a single device

[mhemeryck]

Monitor a single file on a single device, trigger the output if the input changes.

If we can do this simple setup, it should be easy to extend to other, more involved cases.

Setup; steps:

1. monitor a single file via the sysfs interface; run in a dedicated thread, communicate over a channel
2. take the event and have it a call another service that toggles the output file

[mhemeryck]

We can extend this later on with e.g.:

• a config in yaml format
• entity models to capture the format
• go beyond a single device
• ...