Add option to check what would be updated/modified without altering any files given current settings

[chadalon]

This way the user can see data about what would get changed/updated (also need to think about how to handle possible incorrect file assignment).

The cached file locations should make it much faster if they decide to actually run it (if this is implemented correctly) -- as long as preferences have not been changed between this check and actual update.

Running it after checking should not spit out a bunch of garbage the user has already seen.