merge from PE's viewer-trunk 'notifications'

indra/llui/llnotifications.cpp

indra/llui/llnotifications.h

indra/newview/CMakeLists.txt

indra/newview/llchannelmanager.cpp

indra/newview/llnotificationstorage.cpp

indra/newview/llnotificationstorage.h

indra/newview/llpanelgroup.h

indra/newview/llscriptfloater.cpp

indra/newview/llscriptfloater.h

indra/newview/lltoastnotifypanel.cpp

indra/newview/llviewermessage.cpp

indra/newview/llviewermessage.h

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