versions: bump to 20.09 and improve NIX_PATH assembly

The NIX_PATH assembly now walks over all keys in the given channel
repositories and assembles a NIX_PATH entry from it. Previously it made
assumptions about a set of hardcoded keys being available, which wasn't
ideal as it didn't allow device-entries.

nix/home-manager/configuration/graphical-fullblown.nix

@@ -36,29 +36,6 @@ in {
     };
 
     packageOverrides = pkgs: with pkgs; {
-      myPython = python37Full.withPackages (ps: with ps; [
-        pep8 yapf flake8
-        # autopep8 (broken)
-        # pylint (broken)
-        ipython
-        llfuse
-        dugong
-        defusedxml
-        wheel
-        pip
-        virtualenv
-        pypi2nix
-        cffi
-        pyopenssl
-        urllib3
-        mistune
-
-        flask
-
-        pyaml
-      ] ++ [
-        pkgs.libffi
-      ]);
     };
   };
 
@@ -101,7 +78,6 @@ in {
       gnome3.gnome-tweak-tool
       xorg.xhost
       dmidecode
-      python36Packages.glances
       evtest
 
       # Archive Managers
@@ -325,7 +301,7 @@ in {
       glib.dev # contains gdbus tool
       alacritty
       roxterm
-      masterpkgs.wally-cli
+      unstablepkgs.wally-cli
       man-pages
 
       # Screen recording