ZX-Spectrum (SCR) format palette

[moroz1999]

At the moment, XNView seems to use a wrong palette for ZX-Spectrum images (SCR format, 6912 bytes long).
This results in incorrect rendering of a some modern pixel graphics from this platform, which rely on a really precise palette to deal with a color limitations of a format.

The correct values are in Wikipedia: https://en.wikipedia.org/wiki/ZX_Spectr ... or_palette
Semi-bright channel values should be 0xCD, full-bright should be 0xFF. It seems like at the moment XNView uses something close to 0xBF for the semi-bright colors.