Add release barcode searches

[ROpdebee]

Re-adds %release-barcode% template token on release pages
Adds Spotify, Discogs, Amazon and IFPI ISRC search links with this barcode as examples.

[jesus2099]

Thanks very much @ROpdebee.
Could you bump version to 2021.2.12?

Also you should know that this script is no longer maintained on matter branch because I have been working on accepting a big PR for months (#244/#488).
The branch over there is not yet fully functional.

But I will of course merge your PR anyway. ☺️👍

[ROpdebee]

Version bumped!

Do you have a checklist of things that need to be done on that branch? It seems like a massive improvement over the current version, so I'd be happy to help out where I can.

[jesus2099]

Thank you very much! :)

There is a checklist at #488 but, for the moment, I prefer restoring stuff myself, there, to fully understand the big bang change, as it's already a PR in the beginning.

I will make a draft PR (it's something I just discovered), which will be easier to follow up than just a branch alone.
No it does not work out well.