Maddin/textures phillipk2x cleanup

This cleans up the phillipk2x shaders and adds some features:

• Overall better formatting of the shader file.
• Shaders that have an alpha channel, like grates, now work properly.
• Decals are now decals and not opaque textures.
• The glow of all light and computer textures has been adjusted to show their respective colour instead of pure white.