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/llinventorybridge.cpp

@@ -140,6 +140,8 @@ struct LLMoveInv
 	void* mUserData;
 };
 
+using namespace LLOldEvents;
+
 // Helpers
 // bug in busy count inc/dec right now, logic is complex... do we really need it?
 void inc_busy_count()