LLViewerRegion WIP: Added all headers that are dragged in.

Most in particular llevents.h, which comes along with
the demand that the old events in llevent.h are put
in a namespace LLOldEvents. Made all changes necessary
to compile the rest of the code again (without changing
the actual code: it's still using the old events).

This patch also removes LLStopWhenHandled and LLStandardSignal
from indra/llui/llnotifications.h because those are
moved to llevents.h. That seems to be the only change
to indra/llui/llnotifications.h that isn't floater related,
so I left the rest of that file alone.

indra/newview/llinventoryactions.cpp

@@ -99,6 +99,8 @@
 #include "statemachine/aifilepicker.h"
 // </edit>
 
+using namespace LLOldEvents;
+
 const std::string NEW_LSL_NAME = "New Script"; // *TODO:Translate? (probably not)
 const std::string NEW_NOTECARD_NAME = "New Note"; // *TODO:Translate? (probably not)
 const std::string NEW_GESTURE_NAME = "New Gesture"; // *TODO:Translate? (probably not)