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/llmessage/CMakeLists.txt

@@ -65,6 +65,7 @@ set(llmessage_SOURCE_FILES
     llregionpresenceverifier.cpp
     llsdappservices.cpp
     llsdhttpserver.cpp
+    llsdmessage.cpp
     llsdmessagebuilder.cpp
     llsdmessagereader.cpp
     llsdrpcclient.cpp
@@ -163,6 +164,7 @@ set(llmessage_HEADER_FILES
     llregionpresenceverifier.h
     llsdappservices.h
     llsdhttpserver.h
+    llsdmessage.h
     llsdmessagebuilder.h
     llsdmessagereader.h
     llsdrpcclient.h