[Voice Update] llfloateractivespeakers.* to llspeakers.*

Condenses the three moderation responders to one.
Adds Speakers settings.
Uses dedicated timer class to track speakers on the list
Adds temporary getSpeakerManager() function to LLFloaterIMPanel to play the role of LLIMModel::getSpeakerManager

indra/newview/CMakeLists.txt

@@ -416,6 +416,7 @@ set(viewer_SOURCE_FILES
     llselectmgr.cpp
     llsky.cpp
     llspatialpartition.cpp
+    llspeakers.cpp
     llsprite.cpp
     llstartup.cpp
     llstatusbar.cpp
@@ -920,6 +921,7 @@ set(viewer_HEADER_FILES
     llsimplestat.h
     llsky.h
     llspatialpartition.h
+    llspeakers.h
     llsprite.h
     llstartup.h
     llstatusbar.h