Allow calling LLNotificationsUtil::add from any thread.

This makes LLStringUtil thread-safe by removing a rather unnecessary
LLFastTimer from LLStringUtil::format.

Same thing for LLTrans::getString and LLTrans::findString, where
even a comment stated that the author wasn't interested in measuring
cpu time at all. In this case I added some code back to make sure
that we're not calling LLTrans::getString() in an inner loop, which
was the reason that the LLFastTimer was added.

Made one string static to avoid 45000 look ups during login, which
kinda triggered the above test.

Finally, LLNotificationsUtil::add is made thread-safe by making
LLNotificationChannelBase::mItems thread-safe and defering a call
to LLNotifications::updateItem to the main thread when called
from another thread (using a little statemachine).

indra/newview/llfolderviewitem.cpp

@@ -1062,7 +1062,7 @@ void LLFolderViewItem::draw()
 				&&	root_is_loading
 				&&	mShowLoadStatus))
 	{
-		std::string load_string = " ( " + LLTrans::getString("LoadingData") + " ) ";
+		static std::string const load_string = " ( " + LLTrans::getString("LoadingData") + " ) ";
 		font->renderUTF8(load_string, 0, right_x, y, sSearchStatusColor,
 						 LLFontGL::LEFT, LLFontGL::BOTTOM, LLFontGL::NORMAL, LLFontGL::NO_SHADOW, 
 						 S32_MAX, S32_MAX, &right_x, FALSE);