Deoldify Vapoursynth filter

[Dan64]

I attached the new version RC21, where I increaded the values of sc_tht_black and sc_tht_white (2 parameters not exported to GUI).

Don't worry about the high sensitivity of sc_threshold. All the similar frames will be discarded by SSIM.
The pre-filter with misc.SCDetect() is necessary only to reduce the number of frames to be analysed by SSIM.

Dan