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/llcommon/llstring.cpp

@@ -36,9 +36,6 @@
 #include <winnls.h> // for WideCharToMultiByte
 #endif
 
-LLFastTimer::DeclareTimer FT_STRING_FORMAT("String Format");
-
-
 std::string ll_safe_string(const char* in)
 {
 	if(in) return std::string(in);
@@ -1190,7 +1187,6 @@ bool LLStringUtil::formatDatetime(std::string& replacement, std::string token,
 template<> 
 S32 LLStringUtil::format(std::string& s, const format_map_t& substitutions)
 {
-	LLFastTimer ft(FT_STRING_FORMAT);
 	S32 res = 0;
 
 	std::string output;
@@ -1263,7 +1259,6 @@ S32 LLStringUtil::format(std::string& s, const format_map_t& substitutions)
 template<> 
 S32 LLStringUtil::format(std::string& s, const LLSD& substitutions)
 {
-	LLFastTimer ft(FT_STRING_FORMAT);
 	S32 res = 0;
 
 	if (!substitutions.isMap())