Automatic Shot detection

[dkuc]

@fijshion
First draft of the GUI work for clickable shots on the time line is on this branch:
https://github.com/dkuc/shadowclip/tree/automaticShotDetection

You just need to actually find the shots here:
https://github.com/dkuc/shadowclip/blob/automaticShotDetection/ShadowClip/services/ShotFinder.cs