add option to filter already owned games interactively.

[mcclurej06]

I have a bunch of games to redeem, and a largish steam library. The fuzzy matching ends up with many false positives/negatives. I would like and option to see a list of the fuzzy matches, and answer y/n if I already own the game. If the match is exact, then it should auto accept that I own the game.

This pull request implements this functionality. Open to feedback, I don't have alot of python experience.