Fix 07.04

- Fixed bug that would insert black into the remapping process even if there was no black in the palette.
- Dither Overlay opacity now is set to 0.03 when first added to an image. Slider has been adjusted to make working with lower opacities more practical.
- Alpha Threshold filter no longer has a opacity slider.
- Internal update of the effects system that will make it easier to add new effects in the future.