Update/Modernize LLAvatarName and LLAvatarNameCache and _EVERYTHING_ they touch

Fairly certain this adds the feature in which the user may click the online notification to open a chat with the user coming online.

Translators may want to look at the xml changes of this change to see what to update

Removes old LegacyMultiAttachmentSupport patch
Moves LLAvatarName-centric functions into LLAvatarName from elsewhere.
Adds boost::signals2::connections to name polling places.
Removes more old icky static callbacks
Merge from Alchemy, credit where due~
Update notifications.xml to have a bunch of the tags from upstream to ease diffing

indra/newview/scriptcounter.cpp

@@ -48,9 +48,7 @@ namespace
 {
 	void countedScriptsOnAvatar(LLStringUtil::format_map_t args, const LLAvatarName& av_name)
 	{
-		std::string name;
-		LLAvatarNameCache::getPNSName(av_name, name);
-		args["NAME"] = name;
+		args["NAME"] = av_name.getNSName();
 		cmdline_printchat(LLTrans::getString("ScriptCountAvatar", args));
 	}
 }