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/llfloateractivespeakers.cpp

@@ -57,6 +57,8 @@
 
 #include "llavatarname.h"
 
+using namespace LLOldEvents;
+
 const F32 SPEAKER_TIMEOUT = 10.f; // seconds of not being on voice channel before removed from list of active speakers
 const F32 RESORT_TIMEOUT = 5.f; // seconds of mouse inactivity before it's ok to sort regardless of mouse-in-view.
 const LLColor4 INACTIVE_COLOR(0.3f, 0.3f, 0.3f, 0.5f);