Display Backlight: automatically adjust to ambient sensor reading

This registers a Task, reading the ambient light sensor once aminute and
adjusting the display backlight accordingly
2 jobs for !266 with autobacklight in 46 seconds (queued for 3 seconds)
latest detached
Status Name Job ID Coverage
  Build
passed build #6502

00:00:29

 
  Test
passed lint #6503

00:00:17