BUGFIX: Trade sometimes crashes if the user-handler doesn't do a Poll() immediately before calling Trade.Ready().  However, there is no reason they should have to remember to do that (even AdminUserHandler forgot it..)
Simple code cleanup
Added a 'OnBotsTradeRequestRejected' callback to UserHandler
BUGFIX: SteamWeb.Request sometimes returning HTML instead of json response.

Also updated the useragent because reasons.