Add silence detector

[bquandt]

Main usage for apop will be to turn it on in the morning and never turn it off.

During lunch or some break on the production, the crew would set their audio output to 0, but apop will still be recording. A cron job should remove these null sequences, but still not break later concatentation nor cameralolopop records....

"silcence would be set per threshold, ie -60db"

[x42]

Added a silence detector (currently in the source, no new debian package yet). theshold is configurable (currently at least -60dB peak on any channel). If the audiolollipop. It still takes all channels into account which does not work if the audiolollipop receives LTC itself.

File are considered possible to clean if an rsync from data from any cameralollipop has been received and the files are older than the last synec data from the cameralollipop. That fails if there are multiple cameras.. A better solution would be to simply delete all files that are silent and simply generate silence when needed.