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/development/python-modules/cement/default.nix

@@ -16,7 +16,7 @@ buildPythonPackage rec {
   disabled = !isPy3k;
 
   meta = with stdenv.lib; {
-    homepage = http://builtoncement.com/;
+    homepage = https://builtoncement.com/;
     description = "A CLI Application Framework for Python.";
     maintainers = with maintainers; [ eqyiel ];
     license = licenses.bsd3;