replaced items.item with items.xml. Cleaned up item_manager
and removed support for different item styles (since it
didn't work anyway)
2) If a swapper item is used while items are swapped, they will
now un-swap.
3) Moved all models and textures from data/items to data/models.
git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@4648 178a84e3-b1eb-0310-8ba1-8eac791a3b58
