SL-9925: Viewer now shows an error message if import from legacy windlight fails.

indra/llinventory/llsettingssky.cpp

indra/llinventory/llsettingswater.cpp

indra/newview/llenvironment.cpp

indra/newview/llenvironment.h

indra/newview/llfloatereditextdaycycle.cpp

indra/newview/llfloaterfixedenvironment.cpp

indra/newview/llsettingsvo.cpp

indra/newview/llsettingsvo.h

indra/newview/skins/default/xui/en/notifications.xml

indra/newview/skins/default/xui/en/strings.xml