Fixes for item removal

Neither Fling nor Natural Gift triggered Unburden.
Mails removed by Knock Off were recyclable and did not trigger Unburden either.
Flinged Air Balloons and Eject Buttons were unaffected by Pick Up.
Implemented function pokemon.tossItem, for removing items that would be affected by Recycle and Pick Up, while detecting the removal and triggering a TossItem event.
Replaced the boolean pokemon.usedItemThisTurn by the object pokemon.lastItemTurnData to track the way in which the item was removed.