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/llui/llview.cpp

@@ -63,6 +63,8 @@
 #include "lldelayeduidelete.h"
 // </edit>
 
+using namespace LLOldEvents;
+
 //HACK: this allows you to instantiate LLView from xml with "<view/>" which we don't want
 static LLRegisterWidget<LLView> r("view");