[Chat] Add Trade Chat

I think a trade channel would be nice. Just as the global channel it can be global but should be restricted that you can only post once in like a minute or so.

This would help greatly if you don't wanna get spammed by all the chit chat in global but still be able to see what other people are offering or looking for.
The once-per-minute-post restriction would prevent it from being flooded by single requests and stuff.

I think this would be really easy to implement too.