Zms/videostream improvements

Support streaming with zms (using ffmpeg) better …

    * ZoneMinder compiles with ffmpeg 0.5..master
    * Make VideoStream class able to stream through ffmpeg better.
    * Ability to use fixed quality instead of fixed bitrate (by specifying bitrate 0...100)
    * Format url parameter supports <format>/<encoder> syntax

See commit message for details.