Fix foreign inventory call
Merge pull request #561 from StormReaper/foreigninvfix

Fix foreign inventory call
Made MyOfferedItems public
Changed Bot.OtherInventory to work with multiple users, fixes #566 and fixes #543
Moved OtherInventory to UserHandler, cleaned up code
Merge pull request #567 from waylaidwanderer/TradePatch

Makes `Trade.MyOfferedItems` public and fixes `Bot.OtherInventory` to work with multiple users/bots.