Telegram Web - Allow Saving Content

Works for any media content on the WebK version: video, voice, music, photo, document.
Also unlocks text selection. Press Ctrl+C to copy it.

Current issues:
- round videos are saved without a file extension (add .mp4 manually)
- voice messages are saved without a file extension (add .ogg manually)

If you're afraid of unsafeWindow, you can remove it from @grant and from the two functions.
I didn't need this permission for Chrome, but added it anyway just to be sure.