Selectable cloud textures

indra/newview/app_settings/settings_alchemy.xml

indra/newview/app_settings/windlight/clouds/Altocumulus.tga

...a/newview/app_settings/windlight/clouds/Cumulo-Nimbus.tga

indra/newview/app_settings/windlight/clouds/Default.tga

indra/newview/app_settings/windlight/clouds/Layered.tga

indra/newview/lldrawpoolwlsky.cpp

indra/newview/lldrawpoolwlsky.h

indra/newview/llviewercontrol.cpp

...iew/skins/default/xui/en/floater_environment_settings.xml