De-duplicate deferred shader code for atmospherics and transport.

indra/llrender/llshadermgr.cpp

.../newview/app_settings/shaders/class1/deferred/alphaF.glsl

...wview/app_settings/shaders/class1/deferred/materialF.glsl

...ew/app_settings/shaders/class1/deferred/softenLightF.glsl

.../app_settings/shaders/class1/windlight/atmosphericsF.glsl

...ew/app_settings/shaders/class2/deferred/softenLightF.glsl

.../app_settings/shaders/class2/windlight/atmosphericsF.glsl

...ttings/shaders/class2/windlight/atmosphericsHelpersF.glsl

...newview/app_settings/shaders/class2/windlight/gammaF.glsl

...iew/app_settings/shaders/class2/windlight/transportF.glsl

indra/newview/llviewershadermgr.cpp