Quick Action #180

Since macOS 10.14, we can now make Quick Actions that show up in Finder. It would be cool to have a GIF quick action that just quickly converts a GIF without any UI, just with some sensible defaults the user could change in a preferences window. This would also allow for batch conversion.

Note: This is not an easy issue. It's expected that you have advanced Swift knowledge and that you do a good job with this. The point of bounties is to save us time, not drag us down in a way too long-running pull request.