Vassilii KHACHATUROV: rain fix, cleanup, read formerly hard-coded values

Vassilii KHACHATUROV: rain fix, cleanup, read formerly hard-coded values
                      from provided node

"* minor redundant gl call in DrawCone2 optimized away (twice per frame)
* corrected the glRotatef() order in drawRain even further (a less
obvious mistake than before, which is noticed by looking skywards and wiggling
the mouse in the view direction change mode)
* all the "magic numbers" used in the rain rendering code have been
provided a default (based on the old hardcoded value) in a form of a
define, and a meaningfully named static member in SGEnviro"