Auto-bump, minor fixes

Doesn't display preview button if previews aren't available, auto-bump added, now automatically loads prices for items added to page after DOM load (see `/addtrade`).
This simply extracts the trade ID and code (code is only used on Dota2Lounge) from the onclick attribute. It's a regular expression that matches `bumpTrade('[any number]','[any code]')`, where the second attribute is optional