Rewrite transcode control scripts

- run_transcoder.sh was greatly simplified. It now runs as a daemon and
  just forks one job at a time.
  Also it now does logrotation.
- Added a transcode-master.sh script
  This is run on the commandline to get status information and to start
  and stop run_transcoder.sh instances.
- Update Readme.md
Fix race condition in transcode script

Protect logrotation with a lock to avoid a race when multiple
transcoders are running simultaneously.
Additionally the size check was moved to its own test block so it only
runs if the logfile actually exists.
Disable SIGINT in queue.sh

We must not allow queue.sh to be interrupted or the queue file could be
corrupted.