- Added possibility for consumers to *not* affect the presentation time (adjustments...

- Added possibility for consumers to *not* affect the presentation time (adjustments in output.cpp made based on the buffer_depths of the consumers) of other consumers. This is good when consumers that are usually spontaneously added and removed during playout (image_consumer, ffmpeg_consumer, streaming_consumer and channel_consumer) are used, because it prevents the lag previously experienced when adding/removing such consumers.
- Fixed streaming_consumer sometimes crashing the server during destruction.