Reenable Automatic Clipping

[SenorPez]

Blackframe detection was removed as an option by
Commit 12f50c0

In order to reenable blackframe detection and automatic clipping, the following criteria must be met:

• Faster. The old implementation was far too slow. Taking 30 minutes to do blackframe detection on a 60 minute video is not acceptable.
• More intuitive. The concept behind the frame detection was solid: Automatically break the video into distinct scenes, and chop the scenes off the front and rear that you don't want. Unfortunately, the exact implementation was not clear to the average user.
• More automated. There are ways to make this more automatic, and they need to be implemented.