Set the audio 'original duration' during initial events parsing

This is the point at which the start/stop events for the audio are
correctly matched up with eachother; doing it later can give
incorrect results if an 'end recording' event was missing from
the events file.
Add the 'mkclean' step for audio-only recordings
RaP: video processing robustness improvements

Makes it handle possibly corrupted video files with less chance of
breakage. Use features from newer ffmpeg release to simplify the video
trimming - in particular, using -ss as an input option is accurate now.
Switch recording processing to use poppler instead of ghostscript
Use the timestamp from the meeting ID to calculate the real start time

With the switch to a different clock source in red5, the timestamps
in the events file are no longer real-time, but are rather in
seconds since computer boot.

The timestamp in the meeting id is still realtime, so use that as
the start time. Calculate the end time by adding the meeting length
to the start time.
Merge pull request #386 from bigbluebutton/recording-updates-merge

Recording updates merge