treewide: Change URLs to HTTPS

Lots of URLs were HTTP redirect to HTTPS. Changed those and checked them
if there's actual content. Inspired by
https://github.com/NixOS/nixpkgs/issues/60004

pkgs/tools/graphics/flam3/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation rec {
 
   meta = with stdenv.lib; {
     description = "Cosmic recursive fractal flames";
-    homepage = http://flam3.com/;
+    homepage = https://flam3.com/;
     maintainers = [ maintainers.nand0p ];
     platforms = platforms.linux;
     license = licenses.cc-by-nc-sa-20;