Add a "Unlist trade" button instead of the seldom used delete post button

A lot of trades are being marked as sold when it's clearly been taken down by the poster after it wasn't selling for a while.

Most people didn't know they can "delete post" instead of making it as sold.

Marking it as sold will pollute the price check feature that tries to present market prices with a whole list of empty sales.

Here is an example where only 1 trade is a real transaction.

This is mostly an issue now because you can't delete a trade once someone has commented on it & people either don't know, or won't wait the 3 days until it's automatically deleted. Once the next update changes this to always allow deletion it shouldn't be as bad.

From dev: this is already coded into the next patch. We're aware that people are marking as sold as a workaround - these 'empty' sales will be purged when this upcoming patch is deployed so don't worry.