Huge engine change, replace all std::shared_ptrs

Create a new shared pointer type stdext::shared_object_ptr and stdext::shared_obj
using boost::intrusive_ptr

Advantages:
 * half memory usage
 * faster and lightweight

Disadvantages:
 * using weak_ptr is not supported anymore
 * compiling seems slower

modules/game_hotkeys/hotkeys_manager.lua

@@ -150,7 +150,7 @@ function onChooseItemMouseRelease(self, mousePosition, mouseButton)
         if tile then
           local thing = tile:getTopMoveThing()
           if thing then
-            item = thing:asItem()
+            item = thing:isItem()
           end
         end
       elseif clickedWidget:getClassName() == 'UIItem' and not clickedWidget:isVirtual() then