Add titanium spawn chance to Item.dat

[Azba]

This took me many attempts to try to even understand how to make a pull request.
I don't know how to github.

This should add a spawn chance for Titanium material items as discussed on the forum.

[Azba]

Note that Titanium is added on the end of the material chance lines because otherwise it causes strange things to happen when the number of possible main materials and possible secondary materials for an item are not the same - if I were to place Titanium in the middle of, say, long swords then what was once a Steel blade with a Steel hilt would now be a Steel blade with... some other hilt.