Fix glowing of megaerebus, erebus fullbright and nyx fullbright

Raw work with Gimp to mostly fix glow part of megaerebus textures (normal map unchanged I don't know how to fix it); it fixes shirt color affecting glow color

Fix glow part of nyx fullbright textures too (which are identical to the erebus fullbright / megaerebus ones); also fix nyx fullbright glow and reflect textures containing erebus name in them

It fixes #2018 (closed)