Fixed: render sorting issues with multiple translucent 3D floors next to each other on different heights

Fixed: the model should be Z-scaled to 0.83 even in unstretched view to ensure that models fit the geometry right (reported by Ozymandias81)

Fixed: reduced magic in Linedef.SafeDistanceToSq - fixes line/sector selection with 0.125mp grid (reported by camaxide)

Fixed: texture copy/paste in the visual mode was detected as failed pasting and caused a beep. (reported by DOOMGABR, abbuw, Turret_Master)

Fixed: the old way of checking for GZDB's directory writability would not work in certain versions of WINE/Mono

Fixed: cutting a thing in visual mode would leave disposed BaseVisualThings in the selection. (reported by DOOMGABR)

Made Skulltag item sprites optional to support default Skulltag+Zandronum config without producing 100 errors

Added: proper GUI tab for color-related sector properties. The tab now hosts Doom64 lighting as well as old color-related things (floor/ceiling glow, light color, fade color and desaturation).

Fixed state lookup logic for sprite guessing; it should always prefer SPRITE_CHECK_STATES to using the random first frame.