Allow copying URL with stripped redirects

[iki]

Hi @newhouse, thanks for a great extension!

On FB, I often want to copy a link and paste it somewhere, but don't want the ugly FB tracking redirect there. Could you please, either:

1. add something like Copy clean link to a link context menu,
2. or strip known redirects from any copied links as suggested in #63.

Another option would be to process all links on page, maybe in a special mode only, like in https://github.com/nokeya/direct-links-out, but option 2 above seems like a simpler and faster choice imo.