Fixed Steamkit2 Compat issue

Updated packages.
Changed .NET framework target.
Added Any CPU compile option to ExampleBot
Fix trade offers

Fix trade offers still using non-HTTPS requests.
Merge pull request #661 from StoneWolf/master

Fix trade offers
Update OfferSession.cs
Merge pull request #664 from vudung45/master

Update OfferSession.cs
Merge pull request #651 from WildCard65/Steamkit2Fixes

Fixed Steamkit2 issues
Fix item removal.
Merge pull request #673 from scholtzm/RemoveItemFix

Fix item removal from trade offer.