For Friday’s iLounge Deal, you can pick up a lifetime license to the Airy YouTube Video Downloader for only $12.99 — that’s 56% off the regular price. This handy app for your Mac lets you grab your favorite YouTube videos for offline viewing, or even just extract the audio portion as MP3 files to listen to on the go. Airy supports saving YouTube videos straight to your desktop in HD and ultra HD quality, and you can even grab multiple…