Market Place thread prefixes

Since XenForo doesn't allow players the option of closing their own threads, I've added some thread prefixes so that you can mark your own thread closed when you're finished with it.

To do this, first click on the dropdown thread prefixes box and deselect "Open", then select "Closed". If you need to re-open your thread at a later date, deselect "Closed" and select "Open" - and don't forget to add a post to your thread saying that it has been updated!