Andrey Alekseenko authored Dec 20, 2021 and Artem Zhmurov committed Dec 20, 2021

Fixed most of the dead links detected by `linkchecker --check-extern` (our CI only checks internal links).

Did not change the links in old Release notes.

Remained dead links are related to the 2007 GROMACS workshop videos hosted at http://tv.funet.fi/medar/, which has been decommissioned a year ago. I see the following options:

- Find newer content.
- Ask the admins to restore the videos from the archive and make it available.
- Poking around, it seems we can download chunks of videos, which can be then glued together and re-hosted somewhere.
- Maybe @erik.lindahl or @berkhess have the videos archived somewhere?