Port host and reminder to SPDX
So I can clean up this mess :)
It actually did not auto-detect the GPL-3.0-or-later so I had to do it manually :(
I didn't port the extension yet as I am not sure how this needs to be done – the extension folder is distributed separately on e.g. Chrome, Firefox stores. Do I need to ship the LICENSES in there, too? Or is in the repo sufficient, or how is that handled? :)