DRTVWR-493 LLAvatarNameCache to singletone

indra/llmessage/llavatarnamecache.cpp

indra/llmessage/llavatarnamecache.h

indra/newview/llappviewer.cpp

indra/newview/llavatarlist.cpp

indra/newview/llfloaterconversationpreview.cpp

indra/newview/llfloaterimcontainer.cpp

indra/newview/llfloaterimnearbychat.cpp

indra/newview/llfloaterpreference.cpp

indra/newview/llimprocessing.cpp

indra/newview/llimview.cpp

indra/newview/llnotificationhandlerutil.cpp

indra/newview/llstartup.cpp

indra/newview/llviewermenu.cpp