Small Fixes & New Override: Generic Inventory

*Added: 'packages' to .gitignore for packages folder generated by NuGet.
*Fixed: SteamTradeDemoHandler.cs error on adding non tradable items to
the trade.
*Fixed: GenericInventory.cs method load() doesn't cleaning items &
descriptions.
*Added: GenericInventory.ItemDescription ToString() override.
Fixed: mispelling in GenericInventory.cs

Fixed a mispelling that mess up all description indexing.
Source: @TheAnthonyNL
Fixed: comment mispell & break misplacement
Merge pull request #1 from gabrielmtzcarrillo/SteamInventory

ddd