Adds IsFreeToPlay() To Inventory.cs #67

Creates a method to check if a user's inventory is free to play. This
fixes Issue #67: https://github.com/Jessecar96/SteamBot/issues/67

Tested on my inventory, and a free to play's inventory.

This does take into effect the comment of a Free to Play can use
Backpack Expanders.
Revert "Adds IsFreeToPlay() To Inventory.cs #67"

This reverts commit 0b0c85fdb8c8f951e3de1a2e3f1ecf52e9cdbb49.
Adds IsFreeToPlay()

Adds a function to determine if a user is FreeToPlay or not.
Merge pull request #179 from gamemaster1494/ExperimentalThings

Adds IsFreeToPlay() Function In Inventory.cs