Revert "Project modernization (#630)"

This code was not tested and breaks in Release builds, reverting to restore
functionality of the nightly. All in-game menus do not work and generating
a world crashes.

This reverts commit a9be52c41a.

Minecraft.Client/NameEntryScreen.cpp

@@ -41,7 +41,7 @@ void NameEntryScreen::buttonClicked(Button button)
     if (button.id == 0 && trimString(name).length() > 1)
     {
         minecraft->saveSlot(slot, trimString(name));
-        minecraft->setScreen(nullptr);
+        minecraft->setScreen(NULL);
 //        minecraft->grabMouse();	// 4J - removed
     }
     if (button.id == 1)