Add rare non-renewable items to the Wandering Trader's loot table.

There are many items in the game that are super rare and non renewable. The latest additions to this growing list are echo shards, Swift Sneak books, and disk fragments, but heart of the sea, sponge, and elytra are also on this list. 

The problem is that many people play on servers where these resources are very limited and many players have no chance of ever finding them because their locations have already been looted. 

The Wandering Trader should be able to have a very low chance to trade these items. If the probability to have these trades is kept low, then the items will still be very rare and not overused.