Window's not clear and transparent

[unit-404]

In game start location have window, that can be destroyed. In Quake 2 XP window's are transparent, with refraction effect. I suggest add same window's for VKPT version. I in general suggest import common effects from Quake 2 XP (and I mean not just blind copy, but rewrite effects for RT version). Yes, mentioned version have no source codes.

[IvanVolosyuk]

I fixed it in my fork: https://github.com/IvanVolosyuk/q2vkpt