Core/Groups: Move all function definition from .h to .cpp

Core/Groups: Remove Group.h dependency from any .h file

--HG--
branch : trunk

src/server/game/Maps/MapManager.cpp

@@ -33,6 +33,7 @@
 #include "ObjectMgr.h"
 #include "Language.h"
 #include "WorldPacket.h"
+#include "Group.h"
 
 extern GridState* si_GridStates[];                          // debugging code, should be deleted some day