Add gear preview to transmogging

[Shredon1]

Would make picking transmog items 10x easier

[Vyperhand]

As discussed in discord, would require changing the NPC from a Gossip interface to a Vendor or custom interface. I would be willing to put a bounty on this one if it were possible.

[Helias]

Now the transmog NPC is a vendor, so I think we can close this discussion, thanks for the suggestion!