GenericInventory and SteamTradeDemoHandler FIXES

@GenericInventory
The change is a mispelling of the word "instanceid", since this was mispelled all instanceids were nulled.
Somehow this fixed it.

@SteamTradeDemoHandler
Note: most changes are made by Visual Studio 2012 itself so only check the changed below this text:

public override void OnTradeInit()
- added coupon support.

public override void OnTradeAddItem(Schema.Item schemaItem,Inventory.Item inventoryItem)
- added bot log warn / error message when a tf2 item or steam item is added. Just for debugging.

public override void OnTradeAccept()
- after trade is completed i fixed the error that people will get : There is already added an item with the same key
- i did this with the usage of the clear method to clear both dictionaries (descriptions and items)

public override void OnTradeClose()
- i added this method in the steamtradedemohandler so that when the user cancels the trade it also clears the dictionaries as method above for same reason.

If things aren't clear please let me know.

P.S. i've talked about the issues before with gabrielmtzcarrillo