Add settings/validations for new advanced atmo settings.

autobuild.xml

indra/cmake/Atmosphere.cmake

indra/llinventory/llsettingsbase.cpp

indra/llinventory/llsettingsbase.h

indra/llinventory/llsettingssky.cpp

indra/llinventory/llsettingssky.h

indra/llrender/CMakeLists.txt

indra/llrender/llatmosphere.cpp

indra/llrender/llatmosphere.h

indra/llrender/llgltexture.h

indra/newview/app_settings/settings.xml

indra/newview/lldrawpoolwlsky.cpp

indra/newview/llsettingsvo.cpp

indra/newview/llviewershadermgr.cpp

indra/newview/llviewertexture.cpp

indra/newview/pipeline.cpp