Improve high bit depth preview

1. Added 2 new high bit depth preview options:
 - HQ YUV to sRGB using Dither_srgb_display
 - Dither to 8-bit YUV using f3kdb or DitherPost (will be used by default if the required plugins are present

2. Faster processing of interleaved formats using:
 - SeparateColumns on Avisynth 2.6+/AVS+
 - FTurn or PointResize on Avisynth 2.5.8

3. Added status bar messages for:
 - input color space (yuv420i10, ...)
 - currently used  preview method 

  To take advantage of this as an existing users, replace "%CS" in your status bar message with "%CSI (%CS) -> %BDC".