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/llcommon/llevent.h

@@ -35,9 +35,12 @@
 #define LL_EVENT_H
 
 #include "llsd.h"
-#include "llmemory.h"
+#include "llpointer.h"
 #include "llthread.h"
 
+namespace LLOldEvents
+{
+
 class LLEventListener;
 class LLEvent;
 class LLEventDispatcher;
@@ -194,4 +197,6 @@ public:
 	LLSD mValue;
 };
 
+} // LLOldEvents
+
 #endif // LL_EVENT_H