* Advanced trading fixes/modifcations
This adds combine currency option to the Advanced trading screen since
@Airwaves man noticed it didn't have a way of doing it.
Updated stringtables with correct "paid" spelling and differing text for
buying/selling.
This also addds proper currency checking/reporting for the log system
that has been introduced, it's untidy but it works, instead of getting
"user bought x for 1000 currency" in a non coins server, it will convert
it to the proper 1 brief 5 10oz gold etc system (uses a new function
z_calcDefaultCurrencyNoImg)
This also adds a check to see if the buy list is empty (as per the
selling list) and returns text to the user informing them.
Re-arranged buy and sell so buy is on top of sell, it's a bit easier to
read then.
* Advanced trading logging change
This was missing from my previous commit, this changes the
server_tradeobject to check if it's being passed a number (single
currency) or text (my logging currency changes)
* Advanced trading rework
Fixes all problems @ebaydayz
