Avoid pfilamps status collisions by reading new status log

The pfilamps allstat command actually invokes that command on the pi. The command actually queries all the hardware. But while running the lamps, the main "process" is also doing that, giving collisions which result in bad data and mangled outputs.

When adding the new HgCd control I made the main process write to a status log, with a single line per sample. If the status command just reads from the end of that there will be no collisions.