ARI: report duration values in LiveRecording objects

ARI: report duration values in LiveRecording objects

This patch adds three new fields to the LiveRecording model:
 - total_duration: the total length of the live recording
 - talking_duration: optional. The duration of talking energy that was
   detected while the recording was made.
 - silence_duration: optional. The duration of silence that was detected while
   the recording was made.

These values are reported in the RecordingFinished ARI event.

When a DSP is enabled on the channel during the recording - which occurs when
the recording is created with max_silence_seconds (indicating that the user
actually cares about how much silence is in the file), we will report the
talking_duration and silence_duration in addition to the total_duration.

Review: https://reviewboard.asterisk.org/r/3770/

ASTERISK-24037 #close
Reported by: Samuel Galarneau

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@419565 65c4cc65-6c06-0410-ace0-fbb531ad65f3