Changes to Inventory.cs

I've added two more attributes to what can be pulled from an item in the trade. I believe this works for both the bot and the user's items.

`public float FloatValue { get; set; }` allows the bot to get crate numbers from a crate, which wasn't possible before.

`public string ContainedItem { get; set; }` allows the bot to get the contents of a Carefully Wrapped Gift. This one hasn't been tested since I didn't have a wrapped gift to test with, but from reading the schema info on the TF2 wiki I believe this will work.